Gcloud

Actually two commits :

- move to extensions over conventions
http://forums.gradle.org/gradle/topics/is_the_new_plugin_extension_approach_the_way_to_go

- add in gcloud functionality
If gcloud raises an exception, that's a bug in gcloud. For normal errors (user, network, service), it prints a message and exits with 1. So, instead of an exception, I think this should just scrape the error message and put it in a string?

Or perhaps this is some java-ism that I don't follow completely.