MB-31810: Allow users to specify memory order in AtomicMonotonic
MB-31810: Allow users to specify memory order in AtomicMonotonic

Allow a user to specify the memory order they wish to use in
AtomicMonotonic by flipping the operator= and store implementations
and supplying an optional memory order. Allow a user to also specify
the memory order for loads and resets.

Change-Id: I8fa7e992b2188e18136404fdca7f8f21d004afde
Reviewed-on: http://review.couchbase.org/102638
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Dave Rigby <a09264da4832c7ff1d3bf1608a19f4b870f93750@couchbase.com>

daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine