Rename "site" to "domain" in code

We deprecated site in favor of domain in user interfaces.
There are still some references to "site" in the code.
This will help prevent confusion for helios developers.
agent: fix supervisor container teardown

When checking for if a container is no longer running, appropriately
deal with ContainerNotFoundException and interpret it as the container
no longer running (obviously, as it no longer even exists).

Saw the helios agent hitting this and logging stack traces for the
ContainerNotFoundException when using helios-testing and TemporaryJobs.
helios-testing: add SPOTIFY_DOMAIN env var

Internal users need this as their containers use SPOTIFY_DOMAIN for
service discovery.
Add backwards compatibility for "site://" in CliConfig
Merge pull request #167 from spotify/dano/testing-add-SPOTIFY_DOMAIN

helios-testing: add SPOTIFY_DOMAIN env var
Merge pull request #166 from spotify/dano/agent-stop-kill-container-fix

agent: fix supervisor container teardown
Merge pull request #165 from spotify/dxia/s/site/domain/g

Rename "site" to "domain" in code
Output valid JSON for multi-domain CLI commands

TODO: Refactor concrete command implementations return an Object that can
then be put into a {"$DOMAIN": $VALUE} dict before json serializing and
returning it.
Merge pull request #152 from spotify/dxia/multi-domain-json

Output valid JSON for multi-domain CLI commands
Make watch command handle multiple targets.

Also adds in the notion of a MultiTargetCommand where the loop
control has to be handled by the command itself, and not Command.