Allow to specify http host with config

[sashayakovtseva]

Real-life example: I was travelling by plane without any network available and was unable to launch sinker as it is.

In this PR:

• add http-host config parameter

Chores:

• fix http port check where we let OS choose the listen port
• separate tcp port check in a separate function, do no use named loop, do not use unbounded loop
• do not explicitly set default values in cmd options
• add space before comments, add dot at the end of comments

[yuzhichang]

Thanks!