When debugging control plane issues or issues pertaining to a linkerd proxy, it can be cumbersome to get logs from affected containers quickly.
This PR adds a new `logs` command to the Linkerd CLI to surface log lines from any container within linkerd's control plane. This feature relies heavily on [stern](https://github.com/wercker/stern), which already provides this behavior. This PR integrates this package into the Linkerd CLI to allow users to quickly retrieve logs whenever they run into issues when using Linkerd.
Signed-off-by: Dennis Adjei-Baah <dennis@buoyant.io>