remove --oldinstallonly: when no old installonly packages, exit with 0

Upstream commit: 87eb5a7

If no old installonly packages are present, then the command succesfully
removed all of them and should exit with 0 and write the message to
stdout instead of stderr.

Resolves: https://issues.redhat.com/browse/RHEL-6424

dnf/cli/commands/remove.py

@@ -124,8 +124,7 @@ def run(self):
                 for pkg in instonly:
                     self.base.package_remove(pkg)
             else:
-                raise dnf.exceptions.Error(
-                    _('No old installonly packages found for removal.'))
+                logger.info(_('No old installonly packages found for removal.'))
             return
 
         # Remove groups.