sweet/harnesses: don't swallow git stderr

Change-Id: I8ad1a29afc9a7784659fa08f04aeaaf48f30c1c3
Reviewed-on: https://go-review.googlesource.com/c/benchmarks/+/600059
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Michael Knyszek <[email protected]>
Auto-Submit: Austin Clements <[email protected]>

sweet/harnesses/common.go

@@ -16,30 +16,35 @@ import (
 func gitShallowClone(dir, url, ref string) error {
 	cmd := exec.Command("git", "clone", "--depth", "1", "-b", ref, url, dir)
 	log.TraceCommand(cmd, false)
+	cmd.Stderr = os.Stderr
 	_, err := cmd.Output()
 	return err
 }
 
 func gitRecursiveCloneToCommit(dir, url, branch, hash string) error {
 	cloneCmd := exec.Command("git", "clone", "--recursive", "--shallow-submodules", "-b", branch, url, dir)
 	log.TraceCommand(cloneCmd, false)
+	cloneCmd.Stderr = os.Stderr
 	if _, err := cloneCmd.Output(); err != nil {
 		return err
 	}
 	checkoutCmd := exec.Command("git", "-C", dir, "checkout", hash)
 	log.TraceCommand(checkoutCmd, false)
+	checkoutCmd.Stderr = os.Stderr
 	_, err := checkoutCmd.Output()
 	return err
 }
 
 func gitCloneToCommit(dir, url, branch, hash string) error {
 	cloneCmd := exec.Command("git", "clone", "-b", branch, url, dir)
 	log.TraceCommand(cloneCmd, false)
+	cloneCmd.Stderr = os.Stderr
 	if _, err := cloneCmd.Output(); err != nil {
 		return err
 	}
 	checkoutCmd := exec.Command("git", "-C", dir, "checkout", hash)
 	log.TraceCommand(checkoutCmd, false)
+	checkoutCmd.Stderr = os.Stderr
 	_, err := checkoutCmd.Output()
 	return err
 }