Update SamzaMonitorService to spawn deamon threads.

Observed in LI production that samza-rest jvm process doesn’t stop after main thread death(due to jetty server failures) since non-deamon threads spawned for `SamzaMonitorService` are alive.

• This affects samza-rest jvm process lifecycle management. To fix this, plugging in ThreadFactory which sets Thread name format & marks them as daemon.
• Shutdown executorService in finally block (in case of any exception & also during normal exit).