Bug 1185562 - Print message saying the mercurial-setup failures unblock mach; r=smacleod

The messaging on this could be bikeshedded. Something is better than
nothing, that's for sure.

tools/mercurial/mach_commands.py

@@ -67,4 +67,8 @@ class VersionControlCommands(object):
             wizard = MercurialSetupWizard(self._context.state_dir)
             result = wizard.run(map(os.path.expanduser, config_paths))
 
+        if result:
+            print('(despite the failure, mach will not nag you to run '
+                  '`mach mercurial-setup`)')
+
         return result