Add "__repr__" method to class "Service"

The class "Service" doesn't have a "__repr__" method which results
in log outputs like:

    DEBUG [...] service = <nova.service.Service object at 0x56eb890>

This is not helpful when analyzing logs. Therefore this change adds a
"__repr__" method.

Change-Id: I49c8b7f0dde298de780808c988e4b50278eed665

nova/service.py

@@ -110,6 +110,15 @@ class Service(service.Service):
         self.conductor_api = conductor.API(use_local=db_allowed)
         self.conductor_api.wait_until_ready(context.get_admin_context())
 
+    def __repr__(self):
+        return "<%(cls_name)s: host=%(host)s, binary=%(binary)s, " \
+               "manager_class_name=%(manager)s>" % {
+                 'cls_name': self.__class__.__name__,
+                 'host': self.host,
+                 'binary': self.binary,
+                 'manager': self.manager_class_name
+                }
+
     def start(self):
         verstr = version.version_string_with_package()
         LOG.info(_LI('Starting %(topic)s node (version %(version)s)'),

nova/tests/unit/test_service.py

@@ -109,6 +109,17 @@ class ServiceTestCase(test.NoDBTestCase):
 
         self.assertTrue(app)
 
+    def test_repr(self):
+        # Test if a Service object is correctly represented, for example in
+        # log files.
+        serv = service.Service(self.host,
+                               self.binary,
+                               self.topic,
+                               'nova.tests.unit.test_service.FakeManager')
+        exp = "<Service: host=foo, binary=nova-fake, " \
+              "manager_class_name=nova.tests.unit.test_service.FakeManager>"
+        self.assertEqual(exp, repr(serv))
+
     def _service_start_mocks(self):
         self.mox.StubOutWithMock(objects.Service, 'create')
         self.mox.StubOutWithMock(objects.Service, 'get_by_host_and_binary')