selftests/capabilities: Fix the test_execve test

commit 796a3bae upstream.

test_execve does rather odd mount manipulations to safely create
temporary setuid and setgid executables that aren't visible to the
rest of the system.  Those executables end up in the test's cwd, but
that cwd is MNT_DETACHed.

The core namespace code considers MNT_DETACHed trees to belong to no
mount namespace at all and, in general, MNT_DETACHed trees are only
barely function.  This interacted with commit 380cf5ba

 ("fs:
Treat foreign mounts as nosuid") to cause all MNT_DETACHed trees to
act as though they're nosuid, breaking the test.

Fix it by just not detaching the tree.  It's still in a private
mount namespace and is therefore still invisible to the rest of the
system (except via /proc, and the same nosuid logic will protect all
other programs on the system from believing in test_execve's setuid
bits).

While we're at it, fix some blatant whitespace problems.

Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Fixes: 380cf5ba

 ("fs: Treat foreign mounts as nosuid")
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Shuah Khan <shuahkh@osg.samsung.com>
Cc: Greg KH <greg@kroah.com>
Cc: linux-kselftest@vger.kernel.org
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>