selftest: tests idmap mapping with idmap_rid

selftest: tests idmap mapping with idmap_rid

This adds two blackbox tests that run wbinfo --sids-to-unix-ids:

o a non-existing SID from the primary domain should return a mapping

o a SID with a bogus (and therefor unknown) domain must not return a mapping

Bug: https://bugzilla.samba.org/show_bug.cgi?id=11961

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Stefan Metzmacher <metze@samba.org>
Autobuild-User(master): Ralph Böhme <slow@samba.org>
Autobuild-Date(master): Fri Apr  7 00:05:02 CEST 2017 on sn-devel-144

(cherry picked from commit b680ceebf85b2403758a0f9e931f1211e9b80e8d)