Create or improve certain startup log messages

Some log events that I think Solr should have when it starts up. All of these should have unique logger names or text strings so that a verbose log can be searched to find them.

• An event indicating when startup is complete. The time to log this is when all cores are loaded/started (or inventoried for lotsOfCores functionality), cloud information is examined and cached as required, background threads started, etc.
  • The log message should included JVM uptime and elapsed time since Solr (the webapp) started.
  • If somebody were to hot-deploy Solr into a running container, the JVM uptime would not be useful information. That should not be common, though.
• One of the things that SolrCloud will do when it starts is determine whether any indexes need recovery operations, and proceed to do those operations. Separate logs indicating when that process starts and when it finishes could be useful. For the finish event, an elapsed time for all recovery operations would be essential. And I think it should log the JVM uptime, like the earlier "startup complete" message.
  • Each individual recovery operation should probably log similar events.