Make screen_service() useful for more than services

screen_service() can currently only be used to launch things that
pass the 'is_service_enabled' check, even though its calling functions
will have already done this.  This removes such check, renames it
to screen_process() and updates its usage elsewhere.

Change-Id: I480a4560a45b131a95c1b2d2d2379aeba542a9bc
Merge "Make screen_service() useful for more than services"
Fix an issue with setting tempest volume vendor_name with spaces

If the volume vendor has spaces in it, for example “Open Source”, we
need to have quotes around the uses of the variables or the behavior
will not be as expected.

Change-Id: Ie1e99b6d6de2313e5b5b5a5d3057c136c9b34601
Merge branch 'master' of https://github.com/openstack-dev/devstack