[hbck2] Add an 'adoption service' for 'Orphaned Regions'

The 'HBCK Report' has a section for 'Orphaned Regions', regions in the filesystem that are no longer referenced by the running hbase. They should have been cleaned up as part of normal processing but for whatever reason, they were not. Usually these are dessicated directories with nothing in them but sometimes they might have an hfile or two. They could have content in recovered.edits directory too.

The "HBCK Report" page outline how to run the bulk load tool. This will pick up any hfiles in the 'Orphan Region' if there is worry that they have been dropped mistakenly.

For the content under 'recovered.edits', the WALPlayer has just been adjusted so it can pick up this content (See over in HBASE-22976).

The 'adoption service' would be run over an orphan region and it would apply the 'bulk load' if hfiles found and the WALPlayer if 'recovered.edits' found... it would then clean up the region directory on successful load after leaving audit so the 'orphan' was cleaned-up.

hbck2 tool would run the adoption service at first. Once we had some experience and confidence that the adoption service was running smoothly, we'd consider integrating it into the catalogjanitor.

The 'adoption service' first gets mention in the body of HBASE-21745