Use elevated context to query DB in VolumeNumberWeigher

Currently tenant would fail to create volume, if cinder uses
VolumeNumberWeigher.

This will elevate tenant to admin privilege, then VolumeNumberWeigher
has the privilege to get volume count of each hosts.

Change-Id: I1aa0e8ad74d37389ad1feecef113ab8e260dfd0f
Closes-Bug: #1594294

cinder/scheduler/weights/volume_number.py

@@ -50,6 +50,7 @@ class VolumeNumberWeigher(weights.BaseHostWeigher):
         We want spreading to be the default.
         """
         context = weight_properties['context']
+        context = context.elevated()
         volume_number = db.volume_data_get_for_host(context=context,
                                                     host=host_state.host,
                                                     count_only=True)

cinder/tests/unit/scheduler/test_volume_number_weigher.py

@@ -23,6 +23,7 @@ from cinder import context
 from cinder.db.sqlalchemy import api
 from cinder.scheduler import weights
 from cinder import test
+from cinder.tests.unit import fake_constants
 from cinder.tests.unit.scheduler import fakes
 from cinder.volume import utils
 
@@ -46,9 +47,16 @@ def fake_volume_data_get_for_host(context, host, count_only=False):
 
 
 class VolumeNumberWeigherTestCase(test.TestCase):
+
     def setUp(self):
         super(VolumeNumberWeigherTestCase, self).setUp()
-        self.context = context.get_admin_context()
+        uid = fake_constants.USER_ID
+        pid = fake_constants.PROJECT_ID
+        self.context = context.RequestContext(user_id=uid,
+                                              project_id=pid,
+                                              is_admin=False,
+                                              read_deleted="no",
+                                              overwrite=False)
         self.host_manager = fakes.FakeHostManager()
         self.weight_handler = weights.HostWeightHandler(
             'cinder.scheduler.weights')