Keystone_user module: fix authentication needs tenant_name too

The keystone client needs to be passed tenant_name when authenticating the
user/password way. Also it needs auth_url instead of endpoint.
This fix adds login_tenant_name as a module parameter which is consistent
with the other OpenStack modules.
Merge pull request #3487 from djoreilly/ks-auth-error

Keystone_user module: fix authentication needs tenant_name too