MB-17475: Print error message when rebalance fails
MB-17475: Print error message when rebalance fails

The rebalance command in couchbase-cli was getting the error
message from the wrong place. The rebalance task has teh error
message not the entire tasks list.

Change-Id: I5700c2e0a445dd7187e3f30a21e8940ad33aa93c
Reviewed-on: http://review.couchbase.org/60293
Reviewed-by: Eben Haber <d1abc94d70526bfcf3e4b0ce727cb9a6fbb52a3a@couchbase.com>
Tested-by: Michael Wiederhold <a17fed27eaa842282862ff7c1b9c8395a26ac320@couchbase.com>

couchbase/couchbase-cli,couchbase/couchbase-cli