Split compose configuration

[sajith]

Resolves #204.

With everything in one compose.yml, local development becomes rather "heavy", especially with a running ElasticSearch instance. By splitting one docker-compose.yml to a compose.yml (which runs MongoDB and SDX Controller), and a compose.bapm.yml (which runs ElasticSearch and BAPM Server), I'm trying to pare down to a minimal SDX Controller instance for local development.

When we want to start/stop everything, we can still do it like so:

$ docker compose -f compose.yml -f compose.bapm.yml up
$ docker compose -f compose.yml -f compose.bapm.yml down

This changes a couple more things also:

• SDX Controller connects to the mongodb service (name provided by Docker networking), and not $MONGO_HOST (the latter is a little more brittle; the former works almost always).
• Drops a couple of unused environment variables.

[coveralls]

Pull Request Test Coverage Report for Build 7630174178

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 37.778%

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Totals
Change from base Build 7617750686:	0.0%
Covered Lines:	517
Relevant Lines:	1225

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💛 - Coveralls