tools:launch: clean user facing message on wrong timeline description

tools:launch: clean user facing message on wrong timeline description

Summary:
Before:

  $ ../gst-editing-services/tools/ges-launch-1.0 -p
  0:00:00.028629728  8155      0x17e1b60 ERROR                default ges-launcher.c:214:_create_timeline: serialized timeline is   -p

  ** (lt-ges-launch-1.0:8155): ERROR **: Could not create timeline, error: Could not find a suitable formatter
  [1]    8155 trace trap (core dumped)  ../gst-editing-services/tools/ges-launch-1.0 -p

  $

After:

  $ GST_DEBUG=0 ges-launch-1.0 -p

  ERROR: Could not create timeline, error: Could not find a suitable formatter

  $

Reviewers: Mathieu_Du

Differential Revision: http://phabricator.freedesktop.org/D95