selftest: Do not enable inbound replication during replica_sync

selftest: Do not enable inbound replication during replica_sync

Instead we should use the forced=True to only do a very specific
replication, and so avoid noise from any other DC also live
on the network.  This extra replication in turn causes (and this
patch fixes) flapping replica_sync tests.

Signed-off-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Garming Sam <garming@catalyst.net.nz>
BUG: https://bugzilla.samba.org/show_bug.cgi?id=12753

Autobuild-User(master): Andrew Bartlett <abartlet@samba.org>
Autobuild-Date(master): Sat Apr 22 05:19:11 CEST 2017 on sn-devel-144

(cherry picked from commit 52349a7e69a933cbfe410241c7ad80d012886e02)