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.
ref: https://review.openstack.org/#/c/314573/

Change-Id: Ifa8e6b004d7ecf03cd4fdc16d61e09d371ef1098

gnocchixyz/gnocchi,sileht/gnocchi,gnocchixyz/gnocchi,leandroreox/gnocchi,sileht/gnocchi,leandroreox/gnocchi