Previously, when there was an exception in the thrasher
main loop, it would log it but ultimately "succeed"
the teuthology task.
Signed-off-by: John Spray <john.spray@redhat.com>
Move the thrasher-specific methods out of CephManager
into MDSThrasher and plumb them into MDSCluster.
Signed-off-by: John Spray <john.spray@redhat.com