Bug 1403012 - Fix TypeError when running python unittests via |mach test|, r=gbrown

Mach test now creates a structured logger and passes it down into all
of the various test harnesses. Except |mach python-test| doesn't use
structured logging yet, so the argument is not expected.

For now, just accept **kwargs and ignore the logger. Eventually we'll
want to get python tests to use structured logging, and we can use it
at that point.

MozReview-Commit-ID: 8LwdbgI0vqR

python/mach_commands.py

@@ -96,7 +96,8 @@ class MachCommands(MachCommandBase):
                          subsuite=None,
                          verbose=False,
                          stop=False,
-                         jobs=1):
+                         jobs=1,
+                         **kwargs):
         self._activate_virtualenv()
 
         def find_tests_by_path():