only generate one clientmanager instance in interactive mode
only generate one clientmanager instance in interactive mode

Currently, we repeated to generate clientmanager instance when run
command in interactive mode. This should be avoided.

Change-Id: I0536a690bc173be38af08a2e4443115532041efd
Closes-Bug: #1383083

dtroyer/python-openstackclient,openstack/python-openstackclient,varunarya10/python-openstackclient,BjoernT/python-openstackclient,BjoernT/python-openstackclient,dtroyer/python-openstackclient,redhat-openstack/python-openstackclient,varunarya10/python-openstackclient,redhat-openstack/python-openstackclient,openstack/python-openstackclient