tasks/mds_journal_migration: create.
tasks/mds_journal_migration: create.

This is for testing the changes to CephFS
journal format, especially the migration
of journals from old to new format.

This is a teuthology task rather than being
a workunit script, because it involves
manipulating services and config during the
procedure.

Signed-off-by: John Spray <a0ab4ec42db5a70bbcbfc74d8971c0305528d92b@inktank.com>

caibo2014/teuthology,caibo2014/teuthology,t-miyamae/teuthology,ivotron/teuthology,robbat2/teuthology,dreamhost/teuthology,zhouyuan/teuthology,michaelsevilla/teuthology,ceph/teuthology,t-miyamae/teuthology,dmick/teuthology,ceph/teuthology,tchaikov/teuthology,ktdreyer/teuthology,dmick/teuthology,yghannam/teuthology,yghannam/teuthology,SUSE/teuthology,robbat2/teuthology,dreamhost/teuthology,zhouyuan/teuthology,michaelsevilla/teuthology,tchaikov/teuthology,SUSE/teuthology,SUSE/teuthology,dmick/teuthology,ivotron/teuthology,ktdreyer/teuthology