Hardening build rules

Now that [this issue](https://code.google.com/p/google-api-java-client/issues/detail?id=867) is resolved, the build is passing. I've had to update a couple of other bits to get PowerMock to run correctly, as well as bumping the versions to current.

PTAL @broady @domesticmouse 
Feels like this should be renamed gradle.properties.sample and put gradle.properties in .gitignore, along with a step in the instructions on copying this file across and filling it in. Unless @broady has a preferred approach?