join: LDAP connection to remote DC can timeout in large join

join: LDAP connection to remote DC can timeout in large join

When joining a very large domain (e.g. 100K users), the replication can
take so long that the LDAP connection to the remote DC times out.

This patch avoids the problem by adding in a sanity-check after the
replication finishes that the LDB connection is still alive. If not,
then we reconnect.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=13612

Signed-off-by: Tim Beale <timbeale@catalyst.net.nz>
Reviewed-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>