test: add barebones /etc/{passwd,group} and an ld.so.conf

Finit now requires being able to query at least for the root user and
group before starting any services.

Also, add support for using libraries installed in /usr/local

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

test/skel/etc/group

@@ -0,0 +1,9 @@
+root:x:0:
+daemon:x:1:
+bin:x:2:
+sys:x:3:
+adm:x:4:
+tty:x:5:
+disk:x:6:
+dialout:x:20:
+nogroup:x:65534: