Also dump system process threads halfway through the watchdog interval

This gives us a snapshot of what the system process was doing after 30 seconds
of apparent inactivity as well as after 1 minute, to help distinguishing actual
deadlocks from too-slow progress, livelock, etc.

Change-Id: I19758861d1b25f298e88788e8f1c7ec7bf828823
2 files changed