Pass only tenant name or ID to keystoneclient

When creating the keystoneclient, we only need to pass the tenant
ID or name, not both

Change-Id: I0dd03759979026daba1be343f7194f9b7e15a589
Cleanup exc.verbose after tests

A couple of tests override the (module level) exc.verbose flag,
but fail to reset it after the test, which leads to failures
if a test expecting non-verbose exception format happens after the
verbose test.

Change-Id: Iac633707e74464f8d6509a0c5aa0cc62da00ce47