fix MultiCache.cache when it's not specifically configured
fix MultiCache.cache when it's not specifically configured

 * expires_in doesn't affect the connection, so still let it share
 * if you can't share, apply the same back-compat logic for servers => url

Change-Id: Ia460d8b23185310f60ae97ba90145b53375dfcf7
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/265299
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
Reviewed-by: Xander Moffatt <27f70fe194da423604e6e0a63a3de19814736fa9@instructure.com>
QA-Review: Xander Moffatt <27f70fe194da423604e6e0a63a3de19814736fa9@instructure.com>
Product-Review: Cody Cutrer <c4fe2b1d90ef8f2548c8aeabfa633434316f0305@instructure.com>

sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms