Creating 2 backends with the same name creates a mess

[Gorka Eguileor]

There's nothing preventing us from accidentally creating multiple Backends with the same name on the same code run. For example 2 lvm backends using the 'lvm' name with different VGs.

This will create a mess in the DB.

Cinderlib should at least prevent that from happening on the same run, even if it cannot prevent it between runs.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/739190

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/739190
Committed: https://git.openstack.org/cgit/openstack/cinderlib/commit/?id=db573863aaf5a836ac63acbd55c42ba7677c0294
Submitter: Zuul
Branch: master

commit db573863aaf5a836ac63acbd55c42ba7677c0294
Author: Gorka Eguileor <email address hidden>
Date: Fri Jul 3 11:15:27 2020 +0200

    Prevent duplicated backend names

    With this patch we prevent us from having duplicated backend names for
    different driver configurations during the same run.

    If we pass the same name and configuration to Backend a second time we
    get the Backend instance that was created on the first call.

    If we pass the same name with a different configuration then we raise an
    exception on the second call.

    Change-Id: I87c14d236d7f2685315e4088db527090680c9523
    Closes-Bug: #1886164