Adding endpoint for log retrieval on the minion

Adding logic for retrieving logs from docker containers.
Usage:
`curl http://10.245.2.2:10250/containerLogs?containerID=c93b7770a0b6`

Related: 
https://github.com/GoogleCloudPlatform/kubernetes/issues/1235#issuecomment-55188947
yes, that should be string of the container ID