Allow user ID for authentication

In Keystone V3 user names are no longer necessarily unique
accross domains.

A user can still authenticate a user in the non default
domain via the V2 API providng they use IDs instead of names.

Tenant_ID is already supported, this change adds support
for user ID

Change-Id: I36ba75f3e67c8cdb959e31923d5e557414ab6f9b
Merge "Allow user ID for authentication"