We allow having the syntax tenant:user in user since this would make
things easier when switching from auth 1.0 to auth 2.0 and not having to
specify a tenant_name.
In the feature we should use the auth functions from keystoneclient and
be done with those changes, we could then auth by user/tenant-ID.
Change-Id: Ie49748105a678fb9369494e77d41d934d57a39a7
