[install UX] go back to using development.nix (#512)

## Summary

With the recent install-UX improvement of #491, we may run into issues
for
existing users. #508 summarizes the issue and has a workaround fix
implemented.
However, it had me thinking whether this is introducing more risk than
we want
for this week.

To summarize, the improvements made in #491 and later in #506 are:
1. #491: use stepper. Install each package individually, instead of
using `development.nix`.
2. #506: stream the output of `nix-env --install`.

This PR makes it so we continue doing #506 to preserve some UX
improvement, but revert #491 to minimize risk.

When I try it in `devbox cloud shell` with `bazel` and `buf`, the
streaming output helps
preserve the feeling of progress being made. The viewer is no longer
left pondering
"is it stuck? is it broken?".

## How was it tested?

- built a linux devbox binary and deployed a custom VM
- did `devbox cloud shell` to that VM:

The following output shows but is printed in a streaming fashion as
opposed
to blank for a long time and then shows up in one-go.
```
Devbox Cloud
Remote development environments powered by Nix

✓ File syncing started
→ Connecting to virtual machine


Installing nix packages. This may take a while...
	installing 'devbox-development'
	these 2 derivations will be built:
	  /nix/store/9yk55y5ywvm4ihnllfa2kcz158bmbfbg-builder.pl.drv
	  /nix/store/xwcvqhd7fd49dndn5wvn2hx2vcxlrkp0-devbox-development.drv
	these 59 paths will be fetched (919.80 MiB download, 1815.57 MiB unpacked):
	  /nix/store/039g378vc3pc3dvi9dzdlrd0i4q93qwf-binutils-2.39
	  /nix/store/0zmylwn0sznzflf137hhqlnnyskr6cdk-openjdk-headless-11.0.15+10
	  /nix/store/1d6ian3r8kdzspw8hacjhl3xkp40g1lj-binutils-wrapper-2.39
	  /nix/store/1dgws25664p544znpc6f1nh9xmjf4ykc-pcre-8.45
	  /nix/store/1gf2flfqnpqbr1b4p4qz2f72y42bs56r-gcc-11.3.0
	  /nix/store/1i5ah27gxx3a3fyjyydfwwzqq8ni33i8-ncurses-6.3-p20220507

    ... // omitted

    /nix/store/y6aj732zm9m87c82fpvf103a1xb22blp-file-5.43
    /nix/store/zdba9frlxj2ba8ca095win3nphsiiqhb-python3-3.10.8
    /nix/store/zlcnmqq14jz5x9439jf937mvayyl63da-xz-5.2.7-bin
  copying path '/nix/store/hlqzdmnprp3cqwmj4zpzllb8aarjkbvb-iana-etc-20220915' from 'https://cache.nixos.org'...
  copying path '/nix/store/2js892db4aspqb06b9hlxmcr0g97gf3z-bazel-deps' from 'https://cache.nixos.org'...
  copying path '/nix/store/039g378vc3pc3dvi9dzdlrd0i4q93qwf-binutils-2.39' from 'https://cache.nixos.org'...
  copying path '/nix/store/a8mhcagrsly7c7mpjrpsnaahk4aax056-bzip2-1.0.8-bin' from 'https://cache.nixos.org'...
  copying path '/nix/store/xwl6y60ffijfbhxb754dlxk3pkjgw0d2-ed-1.18' from 'https://cache.nixos.org'...
  copying path '/nix/store/a1ad8qiqqb9fpg5a9rhlkm44s02sr61p-expand-response-params' from 'https://cache.nixos.org'...
    
    ... // omitted
```

Author: savil

internal/impl/devbox.go

@@ -5,7 +5,6 @@
 package impl
 
 import (
-	"bufio"
 	"fmt"
 	"io"
 	"os"
@@ -30,7 +29,6 @@ import (
 	"go.jetpack.io/devbox/internal/planner/plansdk"
 	"go.jetpack.io/devbox/internal/plugin"
 	"go.jetpack.io/devbox/internal/telemetry"
-	"go.jetpack.io/devbox/internal/ux/stepper"
 	"golang.org/x/exp/slices"
 )
 
@@ -669,111 +667,28 @@ func (d *Devbox) installNixProfile() (err error) {
 				_ = d.copyFlakeLockToDevboxLock()
 			}
 		}()
-
-		cmd.Env = nix.DefaultEnv()
-
-		debug.Log("Running command: %s\n", cmd.Args)
-		_, err = cmd.Output()
-
-		var exitErr *exec.ExitError
-		if errors.As(err, &exitErr) {
-			return errors.Errorf("running command %s: exit status %d with command stderr: %s",
-				cmd, exitErr.ExitCode(), string(exitErr.Stderr))
-		}
-		if err != nil {
-			return errors.Errorf("running command %s: %v", cmd, err)
-		}
-
-		return nil
+	} else { // Non flakes:
+		cmd = exec.Command(
+			"nix-env",
+			"--profile", profileDir,
+			"--install",
+			"-f", filepath.Join(d.projectDir, ".devbox/gen/development.nix"),
+		)
 	}
 
-	// Non flakes below:
-
-	// Append an empty string to warm the nixpkgs cache
-	packages := append([]string{""}, d.cfg.Packages...)
-
-	total := len(packages)
-	for idx, pkg := range packages {
-		stepNum := idx + 1
-
-		var msg string
-		if pkg == "" {
-			msg = fmt.Sprintf("[%d/%d] nixpkgs", stepNum, total)
-		} else {
-			msg = fmt.Sprintf("[%d/%d] %s", stepNum, total, pkg)
-		}
-
-		step := stepper.Start(d.writer, msg)
-
-		// TODO savil. hook this up to gcurtis's mirrorURL
-		nixPkgsURL := fmt.Sprintf("https://github.com/nixos/nixpkgs/archive/%s.tar.gz", d.cfg.Nixpkgs.Commit)
-
-		var cmd *exec.Cmd
-		if pkg != "" {
-			cmd = exec.Command(
-				"nix-env",
-				"--profile", profileDir,
-				"-f", nixPkgsURL,
-				"--install",
-				"--attr", pkg,
-			)
-		} else {
-			cmd = exec.Command(
-				"nix-instantiate",
-				"--eval",
-				"--attr", "path",
-				nixPkgsURL,
-			)
-		}
-
-		cmd.Env = nix.DefaultEnv()
+	cmd.Env = nix.DefaultEnv()
+	cmd.Stdout = d.writer
+	cmd.Stderr = d.writer
+	err = cmd.Run()
 
-		// Get a pipe to read from standard out
-		pipe, err := cmd.StdoutPipe()
-		if err != nil {
-			return errors.New("unable to open stdout pipe")
-		}
-
-		// Use the same writer for standard error
-		cmd.Stderr = cmd.Stdout
-
-		// Make a new channel which will be used to ensure we get all output
-		done := make(chan struct{})
-
-		// Create a scanner which scans pipe in a line-by-line fashion
-		scanner := bufio.NewScanner(pipe)
-
-		// Use the scanner to scan the output line by line and log it
-		// It's running in a goroutine so that it doesn't block
-		go func() {
-
-			// Read line by line and process it
-			for scanner.Scan() {
-				line := scanner.Text()
-				step.Display(fmt.Sprintf("%s   %s", msg, line))
-			}
-
-			// We're all done, unblock the channel
-			done <- struct{}{}
-		}()
-
-		// Start the command and check for errors
-		if err := cmd.Start(); err != nil {
-			step.Fail(msg)
-			return errors.Errorf("error starting command %s: %v", cmd, err)
-		}
-
-		// Wait for all output to be processed
-		<-done
-
-		// Wait for the command to finish
-		if err = cmd.Wait(); err != nil {
-			step.Fail(msg)
-			return errors.Errorf("error running command %s: %v", cmd, err)
-		}
-		step.Success(msg)
+	var exitErr *exec.ExitError
+	if errors.As(err, &exitErr) {
+		return errors.Errorf("running command %s: exit status %d with command stderr: %s",
+			cmd, exitErr.ExitCode(), string(exitErr.Stderr))
+	}
+	if err != nil {
+		return errors.Errorf("running command %s: %v", cmd, err)
 	}
-
 	return nil
 }