Remove the UNKNOWN release fallback
Remove the UNKNOWN release fallback

When the git_repo_info isn't fetched properly, the playbooks should fail
instead of silently continuing with a "UNKNOWN" value.

Signed-off-by: Jean-Philippe Evrard <jean-philippe.evrard@rackspace.co.uk>

Connected #1397

mancdaz/rpc-openstack,robb-romans/rpc-openstack,sigmavirus24/rpc-openstack,git-harry/rpc-openstack,git-harry/rpc-openstack,sigmavirus24/rpc-openstack,sigmavirus24/rpc-openstack,jacobwagner/rpc-openstack,shannonmitchell/rpc-openstack,prometheanfire/rpc-openstack,prometheanfire/rpc-openstack,BjoernT/rpc-openstack,cfarquhar/rpc-openstack,cloudnull/rpc-openstack,rcbops/rpc-openstack,shannonmitchell/rpc-openstack,mancdaz/rpc-openstack,galstrom21/rpc-openstack,cloudnull/rpc-openstack,galstrom21/rpc-openstack,cfarquhar/rpc-openstack,robb-romans/rpc-openstack,major/rpc-openstack,hughsaunders/rpc-openstack,hughsaunders/rpc-openstack,jacobwagner/rpc-openstack,sigmavirus24/rpc-openstack,BjoernT/rpc-openstack,rcbops/rpc-openstack,major/rpc-openstack