[Tests] RecoveryWhileUnderLoadTests - made sure background indexing threads are closed on errors.

Fixed minor logging discrepancies introduced with randomized shard count.
Added logging to recoverWhileUnderLoadWithNodeShutdown
Added logging ElasticsearchIntegrationTest.allowNodes to indicate what nodes were excluded.
recoverWhileRelocating's shard setting were potentially ignored (depending on key order in hashmaps)