is part of 3.8 during branching.

commit 0d23f5207337fa54be57939eb8d70fe835d4658b
Author: Joseph Fernandes <josferna>
Date:   Tue Apr 26 06:10:16 2016 +0530

    tier/migrator: Fetch the next query file for the next cycle
    
    Problem: When we spawn promote and demote thread, query files
    are build. And only query file with index 0 is picked for migration
    as the first query file. This may not be suitable for scenarios,
    where the file in the query are too big to move in the first cycle,
    as a result file in the other query files always get missed. We need to
    shuffle so that other query files also get a chance.
    
    Fix: Remember the previous first query file and shift it by one index,
    before the migration starts.
    
    Change-Id: I704947bcf4bab6b20b1179a6d9ae4a15a3d51bd9
    BUG: 1330353
    Signed-off-by: Joseph Fernandes <josferna>
    Reviewed-on: http://review.gluster.org/14068
    Tested-by: Joseph Fernandes
    Smoke: Gluster Build System <jenkins.com>
    CentOS-regression: Gluster Build System <jenkins.com>
    Reviewed-by: Dan Lambright <dlambrig>
    Tested-by: Dan Lambright <dlambrig>
    NetBSD-regression: NetBSD Build System <jenkins.org>