Add --as-job-runner: With this flag hivemind will let processes exit gracefully, and wait for all to complete

Example:

```shellsession
hivemind --as-job-runner --exit-with-highest-exit-code - <<PROCFILE
job1: echo "job1 is running"; sleep 0.5; echo "Done"
job2: echo "job2 is running"; sleep 1; echo "Done"
PROCFILE

hivemind --as-job-runner --exit-with-highest-exit-code - <<PROCFILE
job1: echo "job1 is running"; sleep 0.5; echo "Fail"; exit 13
job2: echo "job2 is running"; sleep 1; echo "Done"
PROCFILE
```

Author: danieroux

hivemind.go

@@ -22,6 +22,7 @@ type hivemindConfig struct {
 	NoPrefix           bool
 	PrintTimestamps    bool
 	ExitWithHighest    bool
+	AsJobRunner        bool
 }
 
 type hivemind struct {
@@ -32,6 +33,7 @@ type hivemind struct {
 	done        chan bool
 	interrupted chan os.Signal
 	timeout     time.Duration
+	jobRunner   bool
 }
 
 func newHivemind(conf hivemindConfig) (h *hivemind) {
@@ -44,6 +46,7 @@ func newHivemind(conf hivemindConfig) (h *hivemind) {
 	}
 
 	h.output = &multiOutput{printProcName: !conf.NoPrefix, printTimestamp: conf.PrintTimestamps}
+	h.jobRunner = conf.AsJobRunner
 
 	entries := parseProcfile(conf.Procfile, conf.PortBase, conf.PortStep)
 	h.procs = make([]*process, 0)
@@ -77,6 +80,12 @@ func (h *hivemind) waitForDoneOrInterrupt() {
 	}
 }
 
+func (h *hivemind) waitForInterrupt() {
+	select {
+	case <-h.interrupted:
+	}
+}
+
 func (h *hivemind) waitForTimeoutOrInterrupt() {
 	select {
 	case <-time.After(h.timeout):
@@ -85,7 +94,11 @@ func (h *hivemind) waitForTimeoutOrInterrupt() {
 }
 
 func (h *hivemind) waitForExit() {
-	h.waitForDoneOrInterrupt()
+	if h.jobRunner {
+		h.waitForInterrupt()
+	} else {
+		h.waitForDoneOrInterrupt()
+	}
 
 	for _, proc := range h.procs {
 		go proc.Interrupt()

main.go

@@ -39,6 +39,7 @@ func main() {
 		cli.BoolFlag{Name: "no-prefix", EnvVar: "HIVEMIND_NO_PREFIX", Usage: "process names will not be printed if the flag is specified", Destination: &conf.NoPrefix},
 		cli.BoolFlag{Name: "print-timestamps, T", EnvVar: "HIVEMIND_PRINT_TIMESTAMPS", Usage: "timestamps will be printed if the flag is specified", Destination: &conf.PrintTimestamps},
 		cli.BoolFlag{Name: "exit-with-highest-exit-code, e", EnvVar: "HIVEMIND_EXIT_WITH_HIGHEST_EXIT_CODE", Usage: "exit hivemind with highest exit code from all processes", Destination: &conf.ExitWithHighest},
+		cli.BoolFlag{Name: "as-job-runner", EnvVar: "HIVEMIND_AS_JOB_RUNNER", Usage: "be a job runner instead: Will wait for all to finish with exit code 0, or fail.", Destination: &conf.AsJobRunner},
 	}
 
 	app.Action = func(c *cli.Context) error {