Provide ability to expose Trove database backups panel regardless of Swift's presence in Keystone catalog

[Mat Lowery]

Currently, the Trove database backups panel is only shown when the user has the openstack.services.object-store permission, which is set when the Swift endpoint is registered in Keystone.

At present, Trove does not consult the catalog for any endpoints, let alone Swift. So today, an operator has the ability to specify the swift_url in trove*.conf without ever registering anything in the catalog. If the operator never registers anything in the catalog, the database backups panel will not be shown, despite fully-functional Trove services.

References:
* https://github.com/openstack/horizon/blob/028332da4acb1ef6b9b9a1026affcf97e5501a84/openstack_dashboard/dashboards/project/database_backups/panel.py#L28
* https://github.com/openstack/django_openstack_auth/blob/b49304d9e75b2ed845b278d80d7fb98ce1e5d73e/openstack_auth/backend.py#L190-L191
* https://github.com/openstack/trove/blob/8b2b08f72da09a4c1a81975f9142060b9e6be6b0/etc/trove/trove-guestagent.conf.sample#L28

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/71686

[OpenStack Infra (hudson-openstack)]

Change abandoned by David Lyle (<email address hidden>) on branch: master
Review: https://review.openstack.org/71686
Reason: This review is > 4 weeks without comment, and failed Jenkins the last time it was checked. We are abandoning this for now. Feel free to reactivate the review by pressing the restore button and leaving a 'recheck' comment to get fresh test results.

[Rob Cresswell (robcresswell-deactivatedaccount)]

Trove is now a plugin