tools/presubmitter: after running a test, output collected stderr lines
tools/presubmitter: after running a test, output collected stderr lines

I just realized that cmd.RunOutputError doesn't output stderr to os.stderr.

I also changed "configuration not found" from stderr to stdout.

Change-Id: I4e1a3a91a962ab47fb4938953b45c215bffeab5b

vanadium/go.devtools,vanadium/go.devtools,vanadium/go.devtools