Bug 1632974 - Handle case where mach Command conditions don't have a __name__ attribute r=glandium

There are `conditions` in tree that are callables but which don't have a `__name__` attribute; for example, `functools.partial` instances don't have a `__name__` since they're effectively anonymous functions. If you get to this branch and one of your `conditions` are that kind of object then you'll get a confusing error message instead of the understandable one we're trying to produce here, so account for that possibility.

Differential Revision: https://phabricator.services.mozilla.com/D72957

python/mach/mach/registrar.py

@@ -54,7 +54,7 @@ class MachRegistrar(object):
     def _condition_failed_message(cls, name, conditions):
         msg = ['\n']
         for c in conditions:
-            part = ['  %s' % c.__name__]
+            part = ['  %s' % getattr(c, '__name__', c)]
             if c.__doc__ is not None:
                 part.append(c.__doc__)
             msg.append(' - '.join(part))