remove common db alaises to db utils

A handful of the functions implemented in neutron.db._utils are exposed
in common_db_mixin as aliases. These are unneeded as they're already
defined elsewhere.

This patch removes the following aliases in common_db_mixin:
- safe_creation
- model_query_scope
- model_query
- resource_fields

It also renames the UT for common db mixin to
test__utils to reflect the fact that its testing functions
from the _utils db module.

NeutronLibImpact

Change-Id: I53cd533f107d950f163ad5b19b47097546a4691d

neutron/db/common_db_mixin.py

@@ -20,13 +20,6 @@ from neutron.db import _resource_extend
 from neutron.db import _utils as ndb_utils
 
 
-# TODO(HenryG): Remove these when available in neutron-lib
-safe_creation = ndb_utils.safe_creation
-model_query_scope = ndb_utils.model_query_scope_is_project
-model_query = ndb_utils.model_query
-resource_fields = ndb_utils.resource_fields
-
-
 # TODO(HenryG): Deprecate and schedule for removal
 class CommonDbMixin(object):
     """Deprecated."""

neutron/db/l3_db.py

@@ -46,7 +46,6 @@ from neutron.db import _model_query as model_query
 from neutron.db import _resource_extend as resource_extend
 from neutron.db import _utils as db_utils
 from neutron.db import api as db_api
-from neutron.db import common_db_mixin
 from neutron.db.models import l3 as l3_models
 from neutron.db import models_v2
 from neutron.db import standardattrdescription_db as st_attr
@@ -249,9 +248,9 @@ class L3_NAT_dbonly_mixin(l3.RouterPluginBase,
         delete = functools.partial(self.delete_router, context)
         update_gw = functools.partial(self._update_gw_for_create_router,
                                       context, gw_info)
-        router_db, _unused = common_db_mixin.safe_creation(context, create,
-                                                           delete, update_gw,
-                                                           transaction=False)
+        router_db, _unused = db_utils.safe_creation(context, create,
+                                                    delete, update_gw,
+                                                    transaction=False)
         new_router = self._make_router_dict(router_db)
         registry.notify(resources.ROUTER, events.AFTER_CREATE, self,
                         context=context, router_id=router_db.id,