Allow host:port to accept connection url format about docker-compose-wait

[vlcinsky]

@ufoscout yes, trying to follow 12-factor application principles, I have configuration parameters, one per backing service, e.g.:

• postgresql url: postgres://user:password@db:5432/dbname
• redis url: redis://user:password@redis_server:4433/0
• rabbitmq url: amqp://user:password@messaging_server:9847/other/params?q=124

Keeping all configuration parameters for single backing service in one connection string seems practical as it can be handled as one item (one can argue, secrets shall be separated, but I would say the whole connection string could be considered a secret)

And my need is to test (on TCP level) availability of those backing services using just these urls. This I do before starting actual dependent process/application.

To keep implementation simple, I would require that the url must:

• explicitly express the port (so that we can ignore the scheme prefix and relevant default ports for such scheme)
• explicitly express the host (so that we can skip the decision, what is the default host)

[ufoscout]

This could be an interesting proposal. Anyway, I would like to think about it a little more.
What is your use case exactly? Do you have a variable with the complete connection string and you want to reuse it?