* add TLSSNI01DualNetworkedServers
* use DualNetworkedServers in certbot/plugins/standalone.py
also, make both servers run on the same port.
* make probe_sni connect on ipv6 and ipv4 using None
* mimic BSD-like conditions to get test coverage
* test ServerManager taking into account BSD systems
* pass tests even if python is compiled without ipv6 support
* Creates SupportedChallengesAction
This fixes#3987 as the call to set_by_default can be removed entirely.
Additionally, logger.warning can be used rather than writing to stderr directly
because #3184 has been resolved and we're guaranteed to having logging setup.
* Move validator to SupportedChallengesAction
supported_challenges_validator was moved to SupportedChallengesAction so
argparse.ArgumentError can be easily used to provide nice error output. Tests
in standalone_test.py were also updated so the module still has 100% test
coverage.
* Better document ArgumentError usage
* CLI flag for forcing interactivity
* add --force-interactive
* Add force_interactive error checking and tests
* Add force_interactive parameter to FileDisplay
* add _can_interact
* Add _return_default
* Add **unused_kwargs to NoninteractiveDisplay
* improve _return_default assertion
* Change IDisplay calls and write tests
* Document force_interactive in interfaces.py
* Don't force_interactive with a new prompt
* Warn when skipping an interaction for the first time
* add specific logger.debug message
* only verify port is available when you actually need it
* refactor code to create achalls
* Test port checks are based on achall
* test that only the port for the requested challenge is checked in standalone
