Send the correct user-agent to Keystone

When we execute an Openstack CLI command, keystone should log in
Keystone access log that the user-agent that made the request was
'python-openstackclient' instead of the default 'python-keystoneclient'.
Therefore, when we create the authentication session we
need to send the explicit user-agent.

Closes-Bug: #1453995

Change-Id: I75087fd4bb1ff1e6f2a911bc70bf8008268276bb

Author: Roxana Gherle

openstackclient/common/clientmanager.py

@@ -30,6 +30,8 @@
 
 PLUGIN_MODULES = []
 
+USER_AGENT = 'python-openstackclient'
+
 
 class ClientCache(object):
     """Descriptor class for caching created client handles."""
@@ -163,6 +165,7 @@ def setup_auth(self):
             auth=self.auth,
             session=request_session,
             verify=self._verify,
+            user_agent=USER_AGENT,
         )
 
         return