Do auth_url.rstrip('/') only if auth_url is set

auth_url can be None, for example, when we use bypass_url.

Also, add rstrip('/') for bypass_url (and management_url), which
is done when management_url is gotten from service catalog.

Change-Id: I4f59cc405386a15f8a266d279b27f279eacdb7f1
Merge "Do auth_url.rstrip('/') only if auth_url is set"