galaxy info displayed 'galaxy_info' section wrong

The output of 'ansible-galaxy info' was formatting the
'galaxy_info' key with one char per line.

Previously, when building the output string, items in
role_info that had a dict for value, the label for
it's key ('galaxy_info' for ex) was being added to
the text list in addition to being appended. Only
the append is needed.

Also added a unit test in test/units/cli/test_galaxy.py,
but skip it on py3 until galaxy is py3 compatible.

fixes #15177

lib/ansible/cli/galaxy.py

@@ -152,7 +152,6 @@ class GalaxyCLI(CLI):
                 continue
 
             if isinstance(role_info[k], dict):
-                text += "\t%s: \n" % (k)
                 text.append(u"\t%s:" % (k))
                 for key in sorted(role_info[k].keys()):
                     if key in self.SKIP_INFO_KEYS: