pool: Replace redundant st/rh jobs remove/kill commands with st/rh kill

Addresses the functionality overlap between the st jobs remove/
rh jobs remove and st jobs kill/rh jobs kill. These commands are
replaced with the new st kill and rh kill commands, respectively.

Addresses a race condition between killing an HSM job and the
start of the HSM script.

Resulting dead code is removed from SimpleJobScheduler. HSM script
invocation is modified to translate return code 143 (sigterm) to
a TimeoutCacheException.

Target: trunk
Require-notes: yes
Require-book: yes
Acked-by: Tigran Mkrtchyan <tigran.mkrtchyan@desy.de>
Patch: http://rb.dcache.org/r/5482/