Show failure for Openstack Storate service_type

The openstack_service_type for the Openstack Storage Service (Swift) currently
defaults to "object-store".  However, if the Swift service is unvailable, the
authenticate_v2 method attempts to call:

    service_type.join ", "

The problem is that the String "object-store" doesn't have a join method.

The new tests show that "object-store" is an invalid service_type, whereas
["object-store"] is a valid service_type.

https://github.com/fog/fog/issues/3112
Update the Openstack Storage service type

Change the Openstack Storage service (Swift) openstack_service_type default value from
"object-store" to ["object-store"].

The problem with "object-store" as an openstack_service_type is that if the
Swift service is unavailable, the authenticate_v2 method will attempt to call:

    service_type.join ", "

This will fail for anything that isn't an array.

Changing the openstack_service_type to an array solves this problem.
Additionally, it keeps the openstack_service_type consistent with all of the
other Openstack services' openstack_service_type default values.

https://github.com/fog/fog/issues/3112
Merge pull request #3113 from blomquisg/issue3112-openstack-storage-service-type

Fix Openstack Storage service_type