kill the flag error writer after 2 seconds

There's no point in trying to track these, they're lost after each test.
Kill them after a short delay so we don't have goroutines from every single
command test to wade through if we have a stack dump.

command/meta.go

@@ -160,13 +160,6 @@ type Meta struct {
 	forceInitCopy    bool
 	reconfigure      bool
 
-	// errWriter is the write side of a pipe for the FlagSet output. We need to
-	// keep track of this to close previous pipes between tests. Normal
-	// operation never needs to close this.
-	errWriter *io.PipeWriter
-	// done chan to wait for the scanner goroutine
-	errScannerDone chan struct{}
-
 	// Used with the import command to allow import of state when no matching config exists.
 	allowMissingConfig bool
 }
@@ -339,23 +332,16 @@ func (m *Meta) flagSet(n string) *flag.FlagSet {
 	// This is kind of a hack, but it does the job. Basically: create
 	// a pipe, use a scanner to break it into lines, and output each line
 	// to the UI. Do this forever.
-
-	// If a previous pipe exists, we need to close that first.
-	// This should only happen in testing.
-	if m.errWriter != nil {
-		m.errWriter.Close()
-	}
-
-	if m.errScannerDone != nil {
-		<-m.errScannerDone
-	}
-
 	errR, errW := io.Pipe()
 	errScanner := bufio.NewScanner(errR)
-	m.errWriter = errW
-	m.errScannerDone = make(chan struct{})
 	go func() {
-		defer close(m.errScannerDone)
+		// This only needs to be alive long enough to write the help info if
+		// there is a flag error. Kill the scanner after a short duriation to
+		// prevent these from accumulating during tests, and cluttering up the
+		// stack traces.
+		time.AfterFunc(2*time.Second, func() {
+			errW.Close()
+		})
 		for errScanner.Scan() {
 			m.Ui.Error(errScanner.Text())
 		}