Properly handle 'resource_id' as None for Gnocchi publisher

This issue is related to [1]. In Python 3 (I did not check exactly in
which version), the following code was throwing an error
`data.sort(key=operator.attrgetter('resource_id'))`. Therefore, this
patch is proposing a solution for such situations to properly handle
samples where the `resource_id` is None. Of course, `resource_id`
cannot be None in Gnocchi. However, that can be properly handled by
removing the metric to be pushed from the `gnocchi_resource.yml` file.
Which is what we were doing when we proposed [1]. The problem is that
the sort is happening before that part of the code is executed, to
decide if the sample should be ignored or not.

[1] https://review.opendev.org/c/openstack/ceilometer/+/746717

Change-Id: Ie8eb42df3d5b9505160c9e9d6b86bdaa9a02d16a
(cherry picked from commit b7c2c7ca96)

ceilometer/tests/unit/publisher/test_gnocchi.py

@@ -375,18 +375,30 @@ class PublisherTest(base.BaseTestCase):
     @mock.patch('ceilometer.publisher.gnocchi.GnocchiPublisher'
                 '.batch_measures')
     def test_unhandled_meter_with_no_resource_id(self, fake_batch):
-        samples = [sample.Sample(
-            name='unknown.meter',
-            unit='GB',
-            type=sample.TYPE_GAUGE,
-            volume=2,
-            user_id='test_user',
-            project_id='test_project',
-            source='openstack',
-            timestamp='2014-05-08 20:23:48.028195',
-            resource_id=None,
-            resource_metadata={}
-        )]
+        samples = [
+            sample.Sample(
+                name='unknown.meter',
+                unit='GB',
+                type=sample.TYPE_GAUGE,
+                volume=2,
+                user_id='test_user',
+                project_id='test_project',
+                source='openstack',
+                timestamp='2014-05-08 20:23:48.028195',
+                resource_id=None,
+                resource_metadata={}),
+            sample.Sample(
+                name='unknown.meter',
+                unit='GB',
+                type=sample.TYPE_GAUGE,
+                volume=2,
+                user_id='test_user',
+                project_id='test_project',
+                source='openstack',
+                timestamp='2014-05-08 20:23:48.028195',
+                resource_id="Some-other-resource-id",
+                resource_metadata={})
+        ]
         url = netutils.urlsplit("gnocchi://")
         d = gnocchi.GnocchiPublisher(self.conf.conf, url)
         d._already_checked_archive_policies = True