Update tree() test, use /usr/sbin instead of /sbin

Seems Debian finally went through with their move to symlink /bin and
/sbin to /usr/bin and /usr/sbin, respectively.

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

tests/tree.c

@@ -7,7 +7,7 @@ int main(void)
 	struct { char *path; int fail; } arr[] = {
 		{ "/etc/passwd", -1 },
 		{ "/dev",         0 },
-		{ "/sbin",        0 },
+		{ "/usr/sbin",    0 },
 	};
 
 	for (i = 0; i < NELEMS(arr); i++) {