Fix for issue #3544 (upgrade fails during verification of replication)

The upgrade process didn't take into account the admin connector: the
"cn=admin data" backend has to be updated with admin connector information.

These changes add a synchronization phase between admin data and
the actually config; The server entry in "cn=admin data" should now
include the following attributes: "adminenabled" and "adminport"

This synchronization occurs during the server startup to take advantage
of the "cn=admin data" replication.
In addition to that, the upgrade process includes a verification step.
During this step, the connection handler was not enabled, but the
replication was. The proposed modification disables replication during
the verification step.