Make use of 'current' apps so RBAC ImplicitRoleField can work during migrations

While a migration is taking place, we can't juse use normal model
references like Role and RolePermission, nor can we use generic foreign
keys without manually referring to the content type and object id
fields.

awx/main/utils.py

@@ -20,6 +20,7 @@ import tempfile
 from rest_framework.exceptions import ParseError, PermissionDenied
 from django.utils.encoding import smart_str
 from django.core.urlresolvers import reverse
+from django.apps import apps
 
 # PyCrypto
 from Crypto.Cipher import AES
@@ -30,7 +31,8 @@ __all__ = ['get_object_or_400', 'get_object_or_403', 'camelcase_to_underscore',
            'get_ansible_version', 'get_ssh_version', 'get_awx_version', 'update_scm_url',
            'get_type_for_model', 'get_model_for_type', 'to_python_boolean',
            'ignore_inventory_computed_fields', 'ignore_inventory_group_removal',
-           '_inventory_updates', 'get_pk_from_dict', 'getattrd', 'NoDefaultProvided']
+           '_inventory_updates', 'get_pk_from_dict', 'getattrd', 'NoDefaultProvided',
+           'get_current_apps', 'set_current_apps']
 
 
 def get_object_or_400(klass, *args, **kwargs):
@@ -556,3 +558,11 @@ def getattrd(obj, name, default=NoDefaultProvided):
             return default
         raise
 
+current_apps = apps
+def set_current_apps(apps):
+    global current_apps
+    current_apps = apps
+
+def get_current_apps():
+    global current_apps
+    return current_apps