Add test for nova-compute and nova-network main database blocks

We block the database objects when conductor is not local for compute
and network, but we don't test this code anywhere because it's in the
main() function of the actual executable.

Fix that.

Change-Id: I5b9343d30e6b4aedb05f0731ba9bdca51d408ba9

nova/tests/unit/cmd/test_cmd_db_blocks.py

@@ -0,0 +1,57 @@
+# Copyright 2016 Red Hat
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import contextlib
+
+import mock
+
+from nova.cmd import compute
+from nova.cmd import network
+from nova import db
+from nova import exception
+from nova import test
+
+
+@contextlib.contextmanager
+def restore_db():
+    orig = db.api.IMPL
+    try:
+        yield
+    finally:
+        db.api.IMPL = orig
+
+
+class ComputeMainTest(test.NoDBTestCase):
+    @mock.patch('nova.utils.monkey_patch')
+    @mock.patch('nova.conductor.api.API.wait_until_ready')
+    @mock.patch('oslo_reports.guru_meditation_report')
+    def _call_main(self, mod, gmr, cond, patch):
+        @mock.patch.object(mod, 'config')
+        @mock.patch.object(mod, 'service')
+        def run_main(serv, conf):
+            mod.main()
+
+        run_main()
+
+    def test_compute_main_blocks_db(self):
+        with restore_db():
+            self._call_main(compute)
+            self.assertRaises(exception.DBNotAllowed,
+                              db.api.instance_get, 1, 2)
+
+    def test_network_main_blocks_db(self):
+        with restore_db():
+            self._call_main(network)
+            self.assertRaises(exception.DBNotAllowed,
+                              db.api.instance_get, 1, 2)