Add more testing for native libraries

Make sure that native library paths have the correct permissions and
owners. Also make it easier to do a "String#startsWith" test so we can
get better errors when it fails.

Change the observer to have more sane semantics with a CountDownLatch
instead of weird synchronization on a local variable.

Change-Id: I2437e5ea886d6e6cb8b4edeab80d6053b79857d4