s4:torture: Fix cleanup of the secrets object in session_key test

s4:torture: Fix cleanup of the secrets object in session_key test

BUG: https://bugzilla.samba.org/show_bug.cgi?id=12433

The test is known to be failing if sealing is turned on in some
circumstances. In this case a secret is created and then the function
dcerpc_fetch_session_key() fails. The secret is not removed!

We use torturesecret-%08x with random() to fill in the number. Sometimes
it happens that random() returns a number we already used. So we end up
trying to create a secret for an entry which already exists and run
into a collision

This change makes sure we always cleanup behind us and do not leave
secret objects we created.

Pair-Programmed-With: Guenther Deschner <gd@samba.org>
Signed-off-by: Andreas Schneider <asn@samba.org>
Signed-off-by: Guenther Deschner <gd@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>
Autobuild-User(master): Jeremy Allison <jra@samba.org>
Autobuild-Date(master): Thu Nov 17 22:30:36 CET 2016 on sn-devel-144