Remove the list_servers_since_test

This test is mostly just a very good way to add new failures. There
are subtleties on the timestamping of servers which means that this
can often return the wrong number of servers. Because of this we
should just delete the test.

If we want something like this we should create a much more sane setup
that includes getting all the servers, determinging some subset that
the filter should return, fetching those, and getting the count.

Change-Id: I5c08ef031043229b76a6800eeaab6d418fc4614f
diff --git a/tempest/api/compute/servers/test_list_servers_negative.py b/tempest/api/compute/servers/test_list_servers_negative.py
index 768cc11..fc60d8c 100644
--- a/tempest/api/compute/servers/test_list_servers_negative.py
+++ b/tempest/api/compute/servers/test_list_servers_negative.py
@@ -13,8 +13,6 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-import datetime
-
 from six import moves
 
 from tempest.api.compute import base
@@ -37,7 +35,6 @@
         # tearDownClass method of the super-class.
         cls.existing_fixtures = []
         cls.deleted_fixtures = []
-        cls.start_time = datetime.datetime.utcnow()
         for x in moves.xrange(2):
             resp, srv = cls.create_test_server()
             cls.existing_fixtures.append(srv)
@@ -127,19 +124,6 @@
         self.assertRaises(exceptions.BadRequest, self.client.list_servers,
                           {'limit': -1})
 
-    @test.attr(type='gate')
-    def test_list_servers_by_changes_since(self):
-        # Servers are listed by specifying changes-since date
-        changes_since = {'changes-since': self.start_time.isoformat()}
-        resp, body = self.client.list_servers(changes_since)
-        self.assertEqual('200', resp['status'])
-        # changes-since returns all instances, including deleted.
-        num_expected = (len(self.existing_fixtures) +
-                        len(self.deleted_fixtures))
-        self.assertEqual(num_expected, len(body['servers']),
-                         "Number of servers %d is wrong in %s" %
-                         (num_expected, body['servers']))
-
     @test.attr(type=['negative', 'gate'])
     def test_list_servers_by_changes_since_invalid_date(self):
         # Return an error when invalid date format is passed