Revert change to get_remote_client()

Changeset Idb4a1487d48af24ebcee8e7a78822b2858c1e90b added tempest
client support to the scenario manager and migrated some tests to
it.  It also modified the original OfficialClientTest's
get_remote_client() to use resource keys instead of attributes.
This breaks any test still dependent on the original functionality,
specifically test_baremetal_basic_ops.

Change-Id: Ie9b3f6ea4180d4206efb016563ca1c6d559ad8c4
Closes-bug: #1360367
Merge "Revert change to get_remote_client()"