The config hash ends up not being a unique identifier of a Service. Additionally, Services may have multiple associated Containers.
``` yaml
# Sample docker-compose.yml
version: "2.2"
services:
named-service:
container_name: 'named-container'
image: 'alpine'
command: 'sh -c "while :; do sleep 1; done"'
anonymous-service:
image: 'alpine'
command: 'sh -c "while :; do sleep 1; done"'
scaled-service:
image: 'alpine'
scale: 3
command: 'sh -c "while :; do sleep 1; done"'
```
``` bash
$ docker-compose config --hash="*"
named-service e6e7c4564dfc435ba96725098c62e6b6cf8da9f0b76b0a08be2baddedad6d007
anonymous-service 254f4815ef36bc9fcc2ce80f82278187c9e233309a4106951551f3692657ce9c
scaled-service 254f4815ef36bc9fcc2ce80f82278187c9e233309a4106951551f3692657ce9c
```
This commit changes how Services are discovered (`docker-compose config --services`), how they're associated (by Container ID, rather than config hash or name), and allows for Services to reference multiple Containers (though only the first is directly used for anything at this time).
Currently the thing most slowing down startup is calling docker-compose config --hash="*"
Even calling docker-compose config --services, which only returns service names, takes
about half a second. So that's the main bottleneck. We could try and directly obtain the
service names, but we'd then need to have our own algorithm for composing all the
docker-compose files being used, and that gives us more stuff to maintain
