MB-9343 rebalance via UPR

- enabled only if compiled with DEBUG_UPR macro set

- for now ignores index_aware_rebalance_disabled flag
  this will be fixed in subsequent commit

Change-Id: I83b3229beea68710c1a602cfa43efd0051b21712
Reviewed-on: http://review.couchbase.org/33277
Tested-by: Artem Stemkovski <artem@couchbase.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>