nsqd: extend --tls-required to allow non-tls on the http port

This allows users to require tls on the https/tcp ports, but to
bypass tls on the http port.

Somebody could set up nsqd on a server, expose the tcp/https ports,
lockdown the http port, and allow localhost programs to post to nsqd
without adding support for certs/ssl.
The reason why is because we wanted to assign back only if this isn't produce an error. The original was correct. Can we unit test some of this outside of running the program itself?