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/ld.so.conf

@@ -0,0 +1,3 @@
+/usr/local/lib
+/usr/lib
+/lib