MB-10327 limit the number of moves simultaneously running on one node

before we limited only the number of real moves (Src =/= Dst) which
caused in some cases reaching the memcached limit on number of open
sockets by executing most of the replica-only moves at the same time

this commit doesn't introduce any additional testing for this fix,
just regression tests

Change-Id: Ifa0714eb4ca738b11f46bcde9a495bec8a8dfdc0
Reviewed-on: http://review.couchbase.org/35637
Tested-by: Artem Stemkovski <artem@couchbase.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>