xbmc: init takes care of reboot and shutdown

when one decides to reboot/shutdown via xbmc GUI, he/she
expects it to happen immediately or with minimal delay.

there are addons (trakt, watchdog) that are known to cause high
(1+ minute) shutdown.

----
16:19:15 T:140287759476608   DEBUG: CAnnouncementManager - Announcement: OnQuit from xbmc
16:19:15 T:140287759476608   DEBUG: GOT ANNOUNCEMENT, type: 8, from xbmc, message OnQuit
16:19:15 T:140287759476608  NOTICE: Storing total System Uptime
16:19:15 T:140287759476608  NOTICE: Saving settings
16:19:15 T:140287759476608  NOTICE: stop all
^^ CJobManager::GetInstance().CancelJobs() comes in
16:19:15 T:140286952978176   DEBUG: Thread JobWorker 140286952978176 terminating (autodelete)
16:19:15 T:140286978156288   DEBUG: Thread JobWorker 140286978156288 terminating (autodelete)
16:19:15 T:140286676150016   DEBUG: Thread JobWorker 140286676150016 terminating (autodelete)
16:19:19 T:140286676150016  NOTICE: Thread FileCache start, auto delete: false
^^ so far so good but this should never happen once CApplication::Stop is called. but it does
16:19:30 T:140286676150016   ERROR: CCurlFile::FillBuffer - Failed: Timeout was reached(28)
16:19:30 T:140286676150016  NOTICE: CCurlFile::FillBuffer - Reconnect, (re)try 1
16:19:50 T:140286676150016   ERROR: CCurlFile::FillBuffer - Failed: Timeout was reached(28)
16:19:50 T:140286676150016  NOTICE: CCurlFile::FillBuffer - Reconnect, (re)try 2
16:20:10 T:140286676150016   ERROR: CCurlFile::FillBuffer - Failed: Timeout was reached(28)
16:20:10 T:140286676150016   ERROR: CCurlFile::FillBuffer - Reconnect failed!
16:20:10 T:140286676150016    INFO: CFileCache::Process - Hit eof.
16:20:10 T:140286676150016   DEBUG: Thread FileCache 140286676150016 terminating
^^ 1 minute shutdown delay..
----

with this patch now xbmc can handle SIGTERM and attempt clean exit, systemd
will take care of the rest if xbmc fails to exit.
xbmc: 5 seconds to exit. no more

5 seconds should be enough to store settings, if
pvrmanager / random addon / service is not yet stopped, we dont care