autorid: make the whole initialization atomic with one transaction.

autorid: make the whole initialization atomic with one transaction.

Originally, there were several writing operations:

- store the range HWM
- store the alloc uid HWM
- store the alloc gid HWM
- store the config
- create mappings for a whole list of wellknown sids

Each of these consisted of its own transaction,
the wellknown preallocation even of one transaction per sid.

This change wrapps all of these in one big transaction.
Thereby making the whole initialization atomic, and
with respect to the creation of the wellknown mappings
also more deterministic.

Signed-off-by: Michael Adam <obnox@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>
Autobuild-User(master): Jeremy Allison <jra@samba.org>
Autobuild-Date(master): Thu Apr  3 02:41:25 CEST 2014 on sn-devel-104