cleaner: Shut down timer thread

Target: trunk
Request: 2.9
Require-notes: yes
Require-book: no
Acked-by: Paul Millar <paul.millar@desy.de>
Patch: http://rb.dcache.org/r/7003/
(cherry picked from commit a966d7ada711f438657622ae616109a3e374fce9)
Merge pull request #575 from gbehrmann/fix/2.9/rb7003

Fix/2.9/rb7003