virt/firewall: NoopFirewallDriver::instance_filter_exists must return…

… True

Otherwise, virt.libvirt.connection.ensure_filtering_rules_for_instance()
results in infinite loop.
And eliminate NullFirewallDriver as it's same to NoopFirewallDriver.
This patch fixes bug 953781.

Change-Id: I7936b3c69e9269041defd1ef7e5dda2de1f96dab

nova/tests/test_libvirt.py

@@ -2091,34 +2091,6 @@ def tearDown(self):
         except Exception:
             pass
 
-    class NullFirewallDriver(base_firewall.FirewallDriver):
-        def __init__(self, get_connection, **kwargs):
-            pass
-
-        def prepare_instance_filter(self, instance, network_info):
-            pass
-
-        def unfilter_instance(self, instance, network_info):
-            pass
-
-        def apply_instance_filter(self, instance, network_info):
-            pass
-
-        def refresh_security_group_rules(self, security_group_id):
-            pass
-
-        def refresh_security_group_members(self, security_group_id):
-            pass
-
-        def refresh_provider_fw_rules(self):
-            pass
-
-        def setup_basic_filtering(self, instance, network_info):
-            pass
-
-        def instance_filter_exists(self, instance, network_info):
-            return True
-
     def _create_instance(self, params=None):
         """Create a test instance"""
         if not params:
@@ -2296,7 +2268,7 @@ def fake_execute(*args, **kwargs):
         self.stubs.Set(self.libvirtconnection, '_create_new_domain',
                        fake_create_new_domain)
         self.stubs.Set(utils, 'execute', fake_execute)
-        fw = self.NullFirewallDriver(None)
+        fw = base_firewall.NoopFirewallDriver()
         self.stubs.Set(self.libvirtconnection, 'firewall_driver', fw)
 
         ins_ref = self._create_instance()
@@ -2321,7 +2293,7 @@ def fake_create_new_domain(xml):
 
         self.stubs.Set(self.libvirtconnection, 'plug_vifs', fake_plug_vifs)
         self.stubs.Set(utils, 'execute', fake_execute)
-        fw = self.NullFirewallDriver(None)
+        fw = base_firewall.NoopFirewallDriver()
         self.stubs.Set(self.libvirtconnection, 'firewall_driver', fw)
         self.stubs.Set(self.libvirtconnection, '_create_new_domain',
                        fake_create_new_domain)

nova/virt/firewall.py

@@ -453,3 +453,6 @@ def _noop(*args, **kwargs):
 
     def __getattr__(self, key):
         return self._noop
+
+    def instance_filter_exists(self, instance, network_info):
+        return True