hibernate work_queue after every piece of work

I.e. because it's state is very small, there's no need allow it to
accumulate tons of garbage

Change-Id: Ic8f35d3ad315f887ebe8949541d0dde88e938203
Reviewed-on: http://review.couchbase.org/31692
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>