Support for keystone auth plugins

This patch allows the user to choose which authentication plugin
to use with the CLI. The arguments needed by the auth plugins are
automatically added to the argument parser.

Change-Id: I330c20ddb8d96b3a4287c68b57c36c4a0f869669
Co-Authored-By: Florent Flament <florent.flament-ext@cloudwatt.com>
Merge branch '108325' into dt-test
Merge branch 'obj-test-end-to-end' into dt-test
Merge branch 'll-api-baseapi' into dt-test
Merge branch 'll-api-object-v1' into dt-test
Merge branch 'identity-ec2-tests' into dt-test