Add health checks for services

[lmakarov]

Docker Compose file format v2.1+ and Docker v1.12.0+ support health checks:
https://docs.docker.com/compose/compose-file/#healthcheck
https://docs.docker.com/engine/reference/builder/#healthcheck

Health checks will eliminate the need of guess work and random sleep x in fin for the services (db and cli primarily).

Here and example of how this can be set up via just the compose file:
http://stackoverflow.com/questions/31746182/docker-compose-wait-for-container-x-before-starting-y/41854997#41854997

[lmakarov]

After implementing a healthcheck for docksal/cli I stumble upon this:
docker/compose#4305 (comment)

Docker has introduced healthchecks support in docker-compose format v2.1 just to then drop it in v3 🤦‍♂️

https://docs.docker.com/compose/compose-file/

There are several things to be aware of when using depends_on:

• depends_on will not wait for db and redis to be “ready” before starting web - only until they have been started. If you need to wait for a service to be ready, see Controlling startup order for more on this problem and strategies for solving it.
• Version 3 no longer supports the condition form of depends_on.
• The depends_on option is ignored when deploying a stack in swarm mode with a version 3 Compose file.

So we can either have this now or the ability to deploy to a swarm mode docker cluster in the future.
Unless docker changes their mind again.