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
This is a utility function, you can always pass the same stream to both the output and err parameters, as you are doing inside the function, we're better off creating a generally useful helper function, rather than one that is hand-crafted to the specifics of returning the data over HTTP.

Additionally, I could easily imagine converting this http function to take a 'json' parameter, which would return structured data that separates the two streams, and places each as a member in a json object.