less logging

log "given up on flapping instance" only once, when the crash signal
arrives. Do not log same when the missing instance is detected (as
opposed to crash signal received).

Change-Id: I7fdd11b3b82c8177900eee7e34b9a6bf2f44d480
do not cache missing_indices calculation

Change-Id: I474894d0c2d5998f68b3f883a6c57d34def35caf