It's possible to disconnect/reconnect to/from the community site

:fork_and_knife: 

There are two facets to this PR:

1. Specify `reconnect: true` in the MySQL connection so that connections are self-healing.
2. Access the connection pool through `Supermarket::CommunitySite.pool` and implement `Supermarket::CommunitySite.connect!` and `Supermarket::CommunitySite.disconnect!` so that chef-legacy clients can disconnect and reconnect with impunity (e.g. when Unicorn forks).