netcmd: Add 'samba-tool domain backup rename' command

netcmd: Add 'samba-tool domain backup rename' command

Add a new command that takes a clone of the domain's DB, and renames the
domain as well. (We rename the domain during the clone because it's
easier to implement - the DRS code handles most of the renaming for us,
as it applies the received replication chunks).

The new option is similar to an online backup, except we also do the
following:
- use the new DCCloneAndRenameContext code to clone the DB
- run dbcheck to fix up any residual old DNs (mostly objectCategory
  references)
- rename the domain's netBIOSName
- add dnsRoot objects for the new DNS realm
- by default, remove the old realm's DNS objects (optional)
- add an extra backupRename marker to the backed-up DB. In the restore
  code, if the backup was renamed, then we need to register the new
  domain's DNS zone at that point (we only know the new DC's host IP
  at the restore stage).

Note that the backup will contain the old DC entries that still use the
old dnsHostname, but these DC entries will all be removed during the
restore, and a new DC will be added with the correct dnsHostname.

Signed-off-by: Tim Beale <timbeale@catalyst.net.nz>
Reviewed-by: Gary Lockyer <gary@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>