Clean imports in code

In some part in the code we import objects.
In the Openstack style guidelines they recommend to import only modules.

http://docs.openstack.org/developer/hacking/#imports

Change-Id: I2eb35dc53f0fdb61c31022bb70293d1df8aaf482

Author: Cao Xuan Hoang

openstackclient/common/client_config.py

@@ -15,15 +15,15 @@
 
 import logging
 
-from os_client_config.config import OpenStackConfig
+from os_client_config import config
 
 
 LOG = logging.getLogger(__name__)
 
 
 # Sublcass OpenStackConfig in order to munge config values
 # before auth plugins are loaded
-class OSC_Config(OpenStackConfig):
+class OSC_Config(config.OpenStackConfig):
 
     def _auth_select_default_plugin(self, config):
         """Select a default plugin based on supplied arguments