Optimize NovaClusterDataModelCollector.add_instance_node

This does two things:

1. Rather than make an API call per server on the host,
   get all of the servers in a single API call by
   filtering on the host. The os-hypervisors API results
   to use make this require a bit of refactoring since
   get_compute_node_by_name does not have the service
   entry in it and get_compute_node_by_id does not have the
   servers entry in it. A TODO is added to clean that up
   with a single call to os-hypervisors once we have the
   support in python-novaclient.

2. Pulls get_node_by_uuid() out of the loop.

A test is added for the nova_helper get_instance_list method
since one did not exist before.

The fake compute node mocks in test_nova_cdmc_execute are
also cleaned up since, as noted above, get_compute_node_by_name
and get_compute_node_by_id don't both return all the details.

Change-Id: Ifd9f83c2f399d4c1765b0c520f4d5a62ad0f5fbd

watcher/tests/common/test_nova_helper.py

@@ -146,6 +146,22 @@ class TestNovaHelper(base.TestCase):
             nova_util.get_compute_node_by_hostname,
             hypervisor_name)
 
+    def test_get_instance_list(self, *args):
+        nova_util = nova_helper.NovaHelper()
+        # Call it once with no filters.
+        with mock.patch.object(nova_util, 'nova') as nova_mock:
+            result = nova_util.get_instance_list()
+            nova_mock.servers.list.assert_called_once_with(
+                search_opts={'all_tenants': True}, limit=-1)
+            self.assertIs(result, nova_mock.servers.list.return_value)
+        # Call it again with filters.
+        with mock.patch.object(nova_util, 'nova') as nova_mock:
+            result = nova_util.get_instance_list(filters={'host': 'fake-host'})
+            nova_mock.servers.list.assert_called_once_with(
+                search_opts={'all_tenants': True, 'host': 'fake-host'},
+                limit=-1)
+            self.assertIs(result, nova_mock.servers.list.return_value)
+
     @mock.patch.object(time, 'sleep', mock.Mock())
     def test_stop_instance(self, mock_glance, mock_cinder, mock_neutron,
                            mock_nova):