Improve and fix the docker-compose experience

[Ginja]

Fixes #61

• Introduces config/credentials.yml.enc.sample
• Introduces RAILS_CREDENTIALS_PATH, which can be used to arbitrarily set which credential file to decrypt on startup. Should only be set when developing locally.
• Updates values for KEY_CLAIM_HOST & KEY_CLAIM_TOKEN
• Updates bootstrap.sh to run bundle exec rake portal:bootstrap, which properly sets up the database
• Fixes MySQL healthcheck

[honkfestival]

@jeffmaher this should fix things for you. There are a few cleanup steps you might want to perform first:

docker-compose down
docker-compose build
rm -rf tmp/mysql

Then the steps to get started:

./bootstrap.sh
docker-compose up

We can follow up with docker-compose documentation updates once #72 merges, but in the meantime, please give these a try!

[jeffmaher]

@Ginja , @honkfestival : It's up and running! Thanks!