selftest: add test for force user and well-known primary group

selftest: add test for force user and well-known primary group

Add a test for connecting to a share with a "force user" whos
primary unix gid maps to a well-known alias.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=11608

Signed-off-by: Uri Simchoni <uri@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>
Autobuild-User(master): Jeremy Allison <jra@samba.org>
Autobuild-Date(master): Thu Nov 19 23:20:36 CET 2015 on sn-devel-104
(cherry picked from commit d451bbaee2e025d4135f686c0f220d6337dbf38e)

Autobuild-User(v4-3-test): Karolin Seeger <kseeger@samba.org>
Autobuild-Date(v4-3-test): Mon Nov 23 15:46:03 CET 2015 on sn-devel-104