Attempt to define test data path relative to project

http://www.gradle.org/docs/current/javadoc/org/gradle/api/Project.html#file(java.lang.Object)
Add travis-ci, hopefully without spamming the BC folks

Pretty sure BouncyCastle needs OpenJDK to build and run tests

I don't know how to register the unsigned JCE provider on Oracle JDK,
OpenJDK doesn't seem to check.