Remove unnecessary self.flags and ConfPatcher

In 'start_service' of nova.test.TestCase,
there is the following statement.

self.useFixture(nova_fixtures.ConfPatcher(host=host))

So it is not necessary to set the 'host' parameter
in configuration in the outside of 'start_service'.

TrivialFix
Change-Id: I01e20309df39b24edef91675d2812201d063f66e

nova/tests/functional/notification_sample_tests/test_instance.py

@@ -46,7 +46,6 @@ class TestInstanceNotificationSampleWithMultipleCompute(
         # server will boot on host1
         fake.set_nodes(['host2'])
         self.addCleanup(fake.restore_nodes)
-        self.useFixture(fixtures.ConfPatcher(host='host2'))
         self.compute2 = self.start_service('compute', host='host2')
 
         actions = [

nova/tests/functional/regressions/test_bug_1595962.py

@@ -64,7 +64,6 @@ class TestSerialConsoleLiveMigrate(test.TestCase):
         self.flags(enabled=False, group="vnc")
         self.flags(enabled=False, group="spice")
         self.flags(use_usb_tablet=False, group="libvirt")
-        self.flags(host="test_compute1")
 
         self.start_service('conductor')
         self.start_service('scheduler')

nova/tests/functional/test_servers.py

@@ -1172,7 +1172,6 @@ class ProviderUsageBaseTestCase(test.TestCase,
         """
         fake.set_nodes([host])
         self.addCleanup(fake.restore_nodes)
-        self.flags(host=host)
         compute = self.start_service('compute', host=host)
         self.computes[host] = compute
         return compute
@@ -2714,8 +2713,6 @@ class ServerUnshelveSpawnFailTests(ProviderUsageBaseTestCase):
     def setUp(self):
         super(ServerUnshelveSpawnFailTests, self).setUp()
         # We only need one compute service/host/node for these tests.
-        fake.set_nodes(['host1'])
-        self.flags(host='host1')
         self.compute1 = self._start_compute('host1')
 
         flavors = self.api.get_flavors()