[release] build/all.bash: build vscode-test-env from the root

build/Dockerfile assumes the docker container is built from the root,
after golang.org/cl/253749. Change `all.bash testlocal` to build
the container image from the root.

Change-Id: I30114c49894a847975cc901efd30bb029f0c79e7
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/254805
Trust: Hyang-Ah Hana Kim <[email protected]>
Trust: Robert Findley <[email protected]>
Run-TryBot: Hyang-Ah Hana Kim <[email protected]>
TryBot-Result: kokoro <[email protected]>
Reviewed-by: Robert Findley <[email protected]>
(cherry picked from commit a5e0287)
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/254747

Author: hyangah

build/all.bash

@@ -56,7 +56,7 @@ run_test() {
 
 run_test_in_docker() {
   echo "**** Building the docker image ***"
-  docker build -t vscode-test-env ./build
+  docker build -t vscode-test-env -f ./build/Dockerfile .
   docker run --workdir=/workspace -v "$(pwd):/workspace" vscode-test-env ci
 }