java: Add a unit test for the Syncbase internal API

This change also updates the build.gradle to build the libsyncbase for
the native platform. The building of all the libs is now triggered
after the preBuild task.

The added unit test can be run using the following command:

  ./gradlew testDebug --tests=io.v.syncbase.internal.InitTest

Change-Id: I4bf365a67b4f844628b7e2be49f85bb8c40d989e
2 files changed