MB-20079: Ensure updateWaketimeIfLessThan performs a compare_exchange
MB-20079: Ensure updateWaketimeIfLessThan performs a compare_exchange

The patch MB-20079: Use std::chrono::steady_clock (ProcessClock) with
changeID: I2fc9688abb782fe2c9e80efb6da840be3643d4a5 introduced a bug
where the waketime could be incorrectly updated, due to not performing
a compare_exchange_strong.

This patch reverts to using a compare_exchange_strong, ensuring that
waketime is only updated if it is less than the input time_point.

Change-Id: Ib68689f9a76c6a0455422c293ad62e9c4d04f3d7
Reviewed-on: http://review.couchbase.org/70027
Reviewed-by: Dave Rigby <a09264da4832c7ff1d3bf1608a19f4b870f93750@couchbase.com>
Tested-by: buildbot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>

couchbase/ep-engine,daverigby/kv_engine,membase/ep-engine,daverigby/ep-engine,membase/ep-engine,daverigby/ep-engine,couchbase/ep-engine,membase/ep-engine,daverigby/kv_engine,daverigby/kv_engine,couchbase/ep-engine,membase/ep-engine,couchbase/ep-engine,daverigby/kv_engine,daverigby/ep-engine,daverigby/ep-engine