Fix: fencer: get current time correctly

f52bc8e1ce (2.1.2) introduced a regression by using clock_gettime() with
CLOCK_MONOTONIC to get the current time. Use qb_util_timespec_from_epoch_get()
instead (which as of this writing uses clock_gettime() with CLOCK_REALTIME if
available, and falls back to gettimeofday() if not).