[INTERNAL] cleaned up ConsistencyWatchdogClient

Made fields private and final, rearranged variable locations (put them
to the top) and removed a dead method. In addition added proper
synchronization.

Change-Id: I70f849c4716d436b39ffdc361d2dd0343bafa4c1
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1857
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>