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: I96d6eaf5eca8b7b4cfc358e957b4e35b74ebfb26

openstack/smaug,openstack/smaug