task/mds_journal_migration: fix cleanup

Previously this was remounting in the background
which meant that if a workunit was executed immediately
afterwards it could put files in the mount dir before
the FS was mounted, causing the mount to fail.

Signed-off-by: John Spray <john.spray@redhat.com>
Remove most ceph-specific tasks. They are in ceph-qa-suite now.

Signed-off-by: Zack Cerza <zack.cerza@inktank.com>
Correctly find both internal and external tasks

Signed-off-by: Zack Cerza <zack.cerza@inktank.com>