path lookup: allow null pointer for name argument

The name argument only contains a pointer to the place in the string where the
basename is. In many sitations, we are not interested in such information.
Declaring a variable just for that is just clutter. Allow it to take a null
parameter.

Signed-off-by: Glauber Costa <glommer@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
fs: implement lutimes

Most of the code is common to utimes. This patch then factors out utimes (now
do_utimes) and sys_utimes to accept a flags paramater, and then implements both
utimes and lutimes based on it.

Signed-off-by: Glauber Costa <glommer@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
tests: return a failure code if tst-utimes fails

tst-utimes.so is currently always returning 0, and relying on strings only to
mark success/failure. It's better to reflect that in the return code.

Signed-off-by: Glauber Costa <glommer@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
tst: increment tst-utimes with lutimes functionality

Signed-off-by: Glauber Costa <glommer@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>