Fix CI configuration, update gradle-wrapper.jar and build-tools

Fix for the issue #94 - avoid CI builds fail due to device not found or random error code 137.
Update build-tools to version 21.1.2.
Add gradle wrapper task to the project build file used to update gradle-wrapper.jar to version 2.2.1.
Update gradle-wrapper.jar binary to version 2.2.1 executing the new task.

Last commit include the new binary and the CI build test. 
I can revert last commit or a project member can execute the task another time to replace it.