thrashers: standardize stop and join method names

thrashers: standardize stop and join method names

Thrashers that do not inherit from ThrasherGreenlet previously used a
method called do_join, which combined stop and join functionality. To
ensure consistency and clarity, we want all thrashers to use separate
stop, join, and stop_and_join methods.

This commit renames methods and implements missing stop and stop_and_join
methods in thrashers that did not inherit from ThrasherGreenlet.

Fixes: https://tracker.ceph.com/issues/66698
Signed-off-by: Nitzan Mordechai <nmordech@redhat.com>