[PATCH: Domain backup and restore samba-tool commands]

[Aaron Haslett]

The previous backup tool patch was rejected on the grounds that we
shouldn't add backup commands without a completed restore tool.  This
patch adds a restore tool and tests it by adding a new testenv target
that runs a backup, restores the backup, then starts up the restored
samba.  The method of restoring a backup by untarring is blocked by
adding a backupDate field to sam.ldb.  Samba init is modified so that
startup will fail if the field is present.  Only a successful restore
will remove the field.  The following is left to do:

* Flag subset of tests to run against the new restore_dc testenv
* Restore tool standalone tests (checks various objects after restore
and runs ldapcmp)

Passed CI run: https://gitlab.com/catalyst-samba/samba/pipelines/24182119