remove hardcode of usage
remove hardcode of usage

Refine the definition of USAGE in control.py

Change-Id: I0f515565455e867384ae179a8eca8e35cb0ff3ad

saeki-masaki/glance,scripnichenko/glance,ozamiatin/glance,paramite/glance,openstack/glance,takeshineshiro/glance,klmitch/glance,rajalokan/glance,openstack/glance,jumpstarter-io/glance,saeki-masaki/glance,darren-wang/gl,vuntz/glance,kfwang/Glance-OVA-OVF,sigmavirus24/glance,dims/glance,wkoathp/glance,stevelle/glance,scripnichenko/glance,sigmavirus24/glance,stevelle/glance,paramite/glance,dims/glance,akash1808/glance,ozamiatin/glance,tanglei528/glance,jumpstarter-io/glance,vuntz/glance,wkoathp/glance,darren-wang/gl,takeshineshiro/glance,JioCloud/glance,redhat-openstack/glance,JioCloud/glance,klmitch/glance,akash1808/glance,redhat-openstack/glance,tanglei528/glance,openstack/glance,kfwang/Glance-OVA-OVF,rajalokan/glance