Don't always load client
Don't always load client

This change load client only when a command requires it.

This avoid to connect to API is not needed and avoid the
auth plugin to ask something, if the user just request help.

Change-Id: I4e184f8ce45c137fdcda77ab95d42b4e695b321d

chungg/python-aodhclient,openstack/python-aodhclient,sileht/python-gnocchiclient,gnocchixyz/python-gnocchiclient,chungg/python-aodhclient,gnocchixyz/python-gnocchiclient