Use a separate thread for services that do NTP lookup

Some services do periodic network time lookups and can wedge the other operations on
BackgroundThread and IO Thread, causing Watchdog to kill the runtime. So best to put
those handlers on separate threads.

Going forward, should convert NTP lookups to be async with callbacks.

Bug: 10646480
Change-Id: I8c7ba6052cb3539575712c2099a706b14ff60196