release version 0.5.0

Merge pull request mesosphere-backup#11 from mesosphere/ubuntu-dind

Add Ubuntu Based DIND Agent

0.3.1 release including upgraded Python packages, Alpine 3.4 and an a…

…rgument for optional Docker daemon options.

update readme with 0.3.0

add apache license

Add Apache License, Version 2.0 with copyright statement to the repo now
that it's separate from https://github.com/mesosphere/jenkins-mesos.