MB-3321: skip timer interval ticks on clock jumps forward

Current understanding of MB-3321 is that due to clock jump forward
(i.e. we were sleeping and suddenly discover "now" is many hours
ahead) timer will tick all interval ticks that need to happen
normally. So it'll suddenly do tons of this ticks, swamping machine
with them.

The fix is detecting clock jump forward by observing how far behind
earliest timer tick is. And if it's 10 intervals behind, we just skip
all of them.

Change-Id: I9d00c69b30f87a26d8d51366a6165953edf0b921
Reviewed-on: http://review.couchbase.org/25551
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>