Automate docker image publishing

[mumoshu]

#17 added Dockerfile which is capable of building custom filebeat image, based of elastic.co/filebeat image, along with awsbeat.

I'd love it if any new tag results in a docker image automatically pubished to dockerhub. Probably we can do that with the script deploy provider.

@s12v Would you mind setting it up?
If you're short on time, I can write .traivls.yml. Then all we need is your DOCKER_USER and DOCKER_PASSWORD within travis env for docker login.

[mumoshu]

I considered docker repository named s12v/awsbeats. However it seems like we will outgrow it after adding support for other beats.

Suppose we have supports for filebeat and metricbeat, we could differentiate them like

• s12v/awsbeats:filebeat-canary and s12v/awsbeats:metricbeat-canary

vs

• s12v/awsbeats-filebeat:canary and s12v/awsbeats-metricbeat:canary

Hopefully we have a dedicated docker org. for awsbeats so that the images look ilke:

• awsbeats/filebeat:canary and awsbeats/metricbeat:canary