Use stock argparse --usage behaviour
Use stock argparse --usage behaviour

optparse would substitute the program name for %prog, but argparse
requires %(prog)s. Also, optparse would print 'Usage:' whereas
argparse prints 'usage:'.

Neither optparse behaviour that's worth retaining, let's just use
the default argparse behaviour.

Change-Id: Ied2acb37c366f1a45aed72b6b76f11e2de23828e

redhat-openstack/pbr,JioCloud/pbr,JioCloud/pbr,klmitch/pbr,WiFast/pbr,emonty/oslo-packaging,redhat-openstack/pbr,WiFast/pbr,varunarya10/pbr,openstack-dev/pbr,openstack-dev/pbr,varunarya10/pbr,citrix-openstack-build/pbr,citrix-openstack-build/pbr,openstack-dev/pbr,klmitch/pbr,emonty/oslo-packaging,citrix-openstack-build/pbr