Add docker test for transifex

[moylop260]

Currently we have a new Dockerfile for transifex bot.

I saw that travis now support docker

We can add a travis job to build the transifex bot image, self-test, auto docker push to oca images

Before of work, your feedback is welcome.

The bad news is the time of each travis job: will increase 5 minutes.
The good news is that we can have the image updated, and test it if is working fine.

[pedrobaeza]

Transifex is out, so we can close.