tests: kill_daemons uses TERM instead of KILL

tests: kill_daemons uses TERM instead of KILL

When called to teardown a test, kill_daemon should use KILL to ensure
all leftovers are removed as quickly as possible to leave a clean state
for the next test. However, when kill_daemons is called to shutdown a
given daemon from within a test, it should use TERM by default so the
daemon has time to notify the MON that it goes down. For instance, if
KILLing an OSD, the mon will still report it as being up although the
calling function probably expects that it will be marked out.

Signed-off-by: Loic Dachary <loic@dachary.org>