replmd: Cache recycle-bin state to avoid DB lookup

replmd: Cache recycle-bin state to avoid DB lookup

By caching the recycle-bin state we can save ~6% of the join time.

Checking whether the recycle-bin is enabled involves an underlying DSDB
search. We do this ~4 times for each link we replicate (twice for the
link source and target). By caching the recycle-bin's state over the
duration of the replication, we can save 1000s of unnecessary DB
searches.

With 5K users this makes the join time ~5 secs faster.

Signed-off-by: Tim Beale <timbeale@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Autobuild-User(master): Tim Beale <timbeale@samba.org>
Autobuild-Date(master): Tue Nov 20 08:40:16 CET 2018 on sn-devel-144