samba-tool/drs: do partial replication when --local is given by default

samba-tool/drs: do partial replication when --local is given by default

The samba-tool drs replicate --local command would previously always do
a full replication. This changes it to only replicate changes it doesn't
have according to appropriate highwatermark if the appropriate repsFrom
attribute exists in the local database, or an uptodateness_vector if one
exists.

Signed-off-by: Bob Campbell <bobcampbell@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Stefan Metzmacher <metze@samba.org>
Pair-programmed-with: Andrew Bartlett <abartlet@samba.org>