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Add online terminal support for Kubernetes

## What does this MR do?

Gives terminal access to kubernetes-deployed environments  via the deployment service

## Are there points in the code the reviewer needs to double check?

## Why was this MR needed?

Part of idea to production

## Screenshots (if relevant)

### `/root/reviewing/environments`

![Screen_Shot_2016-12-15_at_19.10.40](/uploads/bd2c54c07b6c85dec3328a20cd185b64/Screen_Shot_2016-12-15_at_19.10.40.png)

### `/root/reviewing/environments/10013`

![Screen_Shot_2016-12-19_at_12.52.39](/uploads/db4e4e06cda88437e8727433d65898b9/Screen_Shot_2016-12-19_at_12.52.39.png)

### `/root/reviewing/enviroments/10013/terminal`

![Screen_Shot_2016-12-15_at_02.35.52](/uploads/1bb77b7e2de2c657ae3bda62dc4f0970/Screen_Shot_2016-12-15_at_02.35.52.png)

## Does this MR meet the acceptance criteria?

- [x] [Changelog entry](https://docs.gitlab.com/ce/development/changelog....