Adding endpoint for log retrieval on the minion

Adding logic for retrieving logs from docker containers.
Usage:
To returns snapshot of the logs:
`curl http://10.245.2.2:10250/containerLogs?containerID=c93b7770a0b6`  

 To tail 15 lines of logs:
`curl http://10.245.2.2:10250/containerLogs?containerID=c93b7770a0b6&tail=15`

To stream logs:
`curl http://10.245.2.2:10250/containerLogs?containerID=c93b7770a0b6&follow=1`

Related: 
https://github.com/GoogleCloudPlatform/kubernetes/issues/1235#issuecomment-55188947
We don't really want to expose that as "docker container ID", we probably want two separate sets of arguments where you can access a container logs by the "attemptID" (which does correspond to the docker container, but is Kube specific) as well as allowing access by podID +  containerName.  So there needs to be a conversion step for the latter where we fetch the pod.