Google releases a new API for automatic deploy to Alpha/Beta and Production channels!
take a look here
Api features:
- Uploading new versions of an app Releasing apps, by assigning APKs to various Tracks (alpha, beta, staged rollout, or production)
- Creating and modifying Google Play Store listings, including localized text and graphics and multi-device screenshots
Updated:
Some java samples about how to use the API: samples
Updated (08-June-2015):
I found and I'm using a gradle plugin that use this API, its called gradle-play-publisher. It is very easy to use, you need only to get a Service account and download a p12 file with a certificate (PlayStore --> Settings --> API access >> "Create Service Account" >> choose p12 format and read instruction in plugin website!