Create runtime descriptor for new service

Instead of explicitly creating proxy for any new service added with 
connection.add_service fill a "run-time" descriptor.
This avoids going into service discovery for each new service (when 
there are multiple of those added in a "init"-like function the overall 
start time increases heavily.

Change-Id: I114ff0ee170244978a1949dc9c7258f373023ab6

openstack/connection.py

@@ -333,11 +333,19 @@ class Connection(six.with_metaclass(_meta.ConnectionMeta,
         # we get an adapter.
         if isinstance(service, six.string_types):
             service = service_description.ServiceDescription(service)
-        service_proxy = service._make_proxy(self)
 
-        # Register the proxy class with every known alias
+        # Directly invoke descriptor of the ServiceDescription
+        def getter(self):
+            return service.__get__(self, service)
+
+        # Register the ServiceDescription class (as property)
+        # with every known alias for a "runtime descriptor"
         for attr_name in service.all_types:
-            setattr(self, attr_name.replace('-', '_'), service_proxy)
+            setattr(
+                self.__class__,
+                attr_name.replace('-', '_'),
+                property(fget=getter)
+            )
 
     def authorize(self):
         """Authorize this Connection

openstack/tests/unit/test_connection.py

@@ -260,6 +260,13 @@ class TestNewService(base.TestCase):
         self.use_keystone_v3(catalog='catalog-v3-fake-v1.json')
         conn = self.cloud
 
+        service = fake_service.FakeService('fake')
+
+        conn.add_service(service)
+
+        # Ensure no discovery calls made
+        self.assertEqual(0, len(self.adapter.request_history))
+
         self.register_uris([
             dict(method='GET',
                  uri='https://fake.example.com',
@@ -272,10 +279,6 @@ class TestNewService(base.TestCase):
                  status_code=404),
         ])
 
-        service = fake_service.FakeService('fake')
-
-        conn.add_service(service)
-
         self.assertEqual(
             'openstack.tests.unit.fake.v1._proxy',
             conn.fake.__class__.__module__)