Prepare to move extension into core plugin

As nova stable_api.rst indicated: As the extension will be removed
from Nove V2.1 REST API. So the concept of core API and extension
API is eliminated also. There is no difference between Nova V2.1
REST API, all of them are part of Nova stable REST API.

so we can move all extensions from contrib to core, this
patch is prelude of https://review.openstack.org/#/c/285213/ and
its following patchs.

Change-Id: Ibd5df4bcc70a4b4854fd519330d89c751f7409dc

novaclient/client.py

@@ -54,6 +54,12 @@ from novaclient import service_catalog
 from novaclient import utils
 
 
+# TODO(jichenjc): when an extension in contrib is moved to core extension,
+# Add the name into the following list, then after last patch merged,
+# remove the whole function
+extensions_ignored_name = ["__init__"]
+
+
 class _ClientConnectionPool(object):
 
     def __init__(self):
@@ -768,7 +774,7 @@ def _discover_via_contrib_path(version):
     for ext_path in glob.iglob(ext_glob):
         name = os.path.basename(ext_path)[:-3]
 
-        if name == "__init__":
+        if name in extensions_ignored_name:
             continue
 
         module = imp.load_source(name, ext_path)