Figure out what it would take for lazily-loaded cores to play nice with SolrCloud

The whole lazy-load core thing was implemented with non-SolrCloud use-cases in mind. There are several user-list threads that ask about using lazy cores with SolrCloud, especially in multi-tenant use-cases.

This is a marker JIRA to investigate what it would take to make lazy-load cores play nice with SolrCloud. It's especially interesting how this all works with shards, replicas, leader election, recovery, etc.

NOTE: This is pretty much totally unexplored territory. It may be that a few trivial modifications are all that's needed. OTOH, It may be that we'd have to rip apart SolrCloud to handle this case. Until someone dives into the code, we don't know.