domain.py: Add schema upgrade option to samba-tool

domain.py: Add schema upgrade option to samba-tool

Microsoft has published the Schema updates that its Adprep.exe tool
applies when it upgrades a 2008R2 schema to 2012R2.

This patch adds an option to samba-tool to go through these update files
and apply each change one by one. Along the way we need to make a few
changes to the LDIF operations, e.g. change 'ntdsschemaadd' to 'add' and
so on.

The bulk of the changes involve parsing the .ldif file and separating
out each update into a separate operation.

There are a couple of errors that we've chosen to ignore:
- Trying to set isDefunct for an object we don't know about.
- Trying to set a value for an attribute OID that we don't know about
  (we may need to fix this in future, but it'll require some help from
   Microsoft about what the OIDs actually are).

To try to make life easier, I've added a ldif_schema_update helper
class. This provides convenient access of the DN the change applies to
and other such details (whether it's setting isDefunct, etc).

Pair-programmed-with: Garming Sam <garming@catalyst.net.nz>

Signed-off-by: Tim Beale <timbeale@catalyst.net.nz>
Signed-off-by: Garming Sam <garming@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>