External test + working SaveKeyringParcel

Moving discussion on the subject here.

So here's the thing. This still requires a snapshot version of the gradle-android-test-plugin. That can be put into the local maven repository by simply running ./install-custom-gradle-plugin.sh, and this works fine in travis as well. It's just hella ugly.

I tried including the Test project conditionally by providing a variable (./gradlew -PwithTesting=true) or checking for a file (touch tests-ok). Both worked fine, but in turn broke the android studio build. I'm out of ideas here.

So tl;dr everything works fine but it's slightly ugly now. What do we do with this? I would like to get this into master one way or another.