Updates to ensure connections are closed in ConnectionManager and tests

[aparod]

• Make sure connections get closed for commands that failed their first attempt
• Update tests to expect the socket being closed
• Update inaccurate README testing instructions

All non-enterprise tests are now passing against the version of Faktory provided in docker-compose.yml.

Note: It's not clear to me if close_connection/1 should be called from other places in FaktoryWorker.ConnectionManager.send_command/3, here and here. Thoughts?

[Ch4s3]

Hey @aparod I just saw this. I'll take a look asap and get back to you.

[Ch4s3]

Lines 46 and 51 do look like places where it should be called.