s4:torture: add a test-suite for VSS

s4:torture: add a test-suite for VSS

This test will not be run from the main torture test runner in selftest,
as there we don't pass the required arguments 'twrp_file' and
'twrp_snapshot'.

The test needs a carefully prepared environment with provisioned
snapshot data, so the test will be started from a blackbox test
script. That comes next.

Bug: https://bugzilla.samba.org/show_bug.cgi?id=13688

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>