Accessible build logs

Adding option to retrieve logs form a build.
Usage:
        `kube buildLogs --id="buildID"`
See the selfLink construction work upstream for an example of how this should work in general.  I'm not sure this is *wrong*, but it's assuming that the API server is hosted at `/` which is not safe.  As part of your constructor you need to take the path prefix for the proxy as a string and then prepend it to this value.