Squash a few deprecation warnings

- inspect.getargspec() -> inspect.getfullargspec()
- register pytest.mark.fixture_args
- replace use of DRF's deprecated NullBooleanField
- fix some usage of naive datetimes in the tests
- fix some strings with backslashes that ought to be raw strings

awx/conf/migrations/_ldap_group_type.py

@@ -17,7 +17,7 @@ def fill_ldap_group_type_params(apps, schema_editor):
     else:
         entry = Setting(key='AUTH_LDAP_GROUP_TYPE_PARAMS', value=group_type_params, created=now(), modified=now())
 
-    init_attrs = set(inspect.getargspec(group_type.__init__).args[1:])
+    init_attrs = set(inspect.getfullargspec(group_type.__init__).args[1:])
     for k in list(group_type_params.keys()):
         if k not in init_attrs:
             del group_type_params[k]