Have rsync based sysvol share replication from existing dc on join

[dafzor]

Samba dc does not sync sysvol share which is essencial for the correct operation of a domain.

Thus the container should do a regular rsync from a given domain controller when joining a domain.

Reference: https://wiki.samba.org/index.php/Rsync_based_SysVol_replication_workaround