MDP-5 Return cached data on ED REST API errors.

In the event of an error communicating with the ED REST API, return a cached metadata document even if it is expired. This behavior would result in increased resiliency for the Login Service given that metadata resolution errors are fatal in the Shibboleth IdP. The cache cleaner facility was removed to facilitate this behavior since cache cleanup is fundamentally incompatible with returning expired metadata. Also increase cache max TTL values since the /build?cache=true endpoint is invoked by service replication, which is a reliable trigger to purge and refresh stale metadata on ED service changes.