Fix `deis run` environment and remove ephemeral container

Two notable changes:

 1. We now construct `-e` flags for `docker run` based on the current release
 2. We now pass `-rm` to `docker run` to ensure the container is removed automatically when it exits

Getting this to show up in testing is a bit tricky, since there are 3 layers of shell interpolation we must contend with:

1. `deis` client shell on the workstation
2. `docker run` command on the host
3. the shell inside the container itself

Proof it now works:
```
$ deis config:set SHELL_INTERPOLATION=hard
=== player-yearling
SHELL_INTERPOLATION: hard
$ deis run 'echo \$SHELL_INTERPOLATION'
hard
```