Remove test_barbican from keymgr tests

Unfortunately it seems we have some very poorly
written keymgr unit tests, specifically
keymgr/test_barbican.py does this:
from barbicanclient.common import auth

First problem is that from a unit test perspective
that pretty much sucks, second problem is that
barbicanclient as of version 3.0.0.0 no longer
has an "auth" module, as a result Cinderunit tests
now fail.

The test_barbican.py unit tests need to be rewritten
to mock out the client components and actually test
Cinder components where needed without relying on
the barbicanclient.

For now in order to free up the gate, remove test_barbican.py

Change-Id: Id770c87c0d622ae4c1e0d71141ffa9aed29be2ec
Partial-Bug: #1389419