logcatd: add stop and clear actions

(cherry pick from commit cd5118bf)

- add stop and clear (and stop) actions to logcatd.rc
- use stop and clear actions in logpersist script

Bug: 28788401
Bug: 28813587
Bug: 28936216
Change-Id: Id05118fb51e40609fd7b3a934cf9302f67ef6d1d