Added support for bind_hostname options.

See also related wptserve PR https://github.com/w3c/wptserve/pull/10
Match new args to start_http_server() to wptserve.
Un-global bind_hostname & pass it properly instead
Don't pass pywebsocket -H if bind_hostname != true
Simplify a bit (in response to jgraham review).
Fixed variable name.
Merge pull request #726 from w3c/submission/sideshowbarker/bind_hostname

Added support for bind_hostname options.