print messages unless the underlying commands actually generate output.
This is a more conservative version of r28271.

  BUG=none
  TEST=none
  R=maruel

Review URL: http://codereview.chromium.org/344004

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@30296 0039d316-1c4b-4281-b951-d872f2087c98