CBSE-1874: Add sequential flag to run backup process
CBSE-1874: Add sequential flag to run backup process

In order to reduce memory hit to server, we'd like to trigger
backup processes in a sequential manner, i.e. create N DCP
streams one batch after another instead of all in the same time.

Change-Id: I76c267498e835e73ae99c0904e39012dd4d78582
Reviewed-on: http://review.couchbase.org/51917
Reviewed-by: Eben Haber <d1abc94d70526bfcf3e4b0ce727cb9a6fbb52a3a@couchbase.com>
Reviewed-by: Bin Cui <ed18693fff32c00e22495f4877a3b901bed09041@gmail.com>
Tested-by: Bin Cui <ed18693fff32c00e22495f4877a3b901bed09041@gmail.com>
Reviewed-on: http://review.couchbase.org/51957

couchbase/couchbase-cli,couchbase/couchbase-cli