remove verbose option in devstack plugin
remove verbose option in devstack plugin

This option is deprecated in Mitaka and has been removed in Newton,
and its default value is True already. Let's remove it.

Change-Id: I167713165bd96a4ccd423976f8fcad5ff8fc399c
ref: https://review.openstack.org/#/c/314573/

openstack/zaqar,openstack/zaqar,openstack/zaqar,openstack/zaqar