fix default debug level in usage output

Signed-off-by: Thomas Stilwell <stilwellt@openlabs.co>
add custom logging level DATADUMP=5

also:

- change one log output to datadump as example
- rename some logger objects for consistency

Signed-off-by: Thomas Stilwell <stilwellt@openlabs.co>
Merge pull request #863 from benemorius/loglevel-datadump

add custom logging level DATADUMP=5
Refactor and test init_additional_STUN_servers.

* Make it accept any server sequence.
* Make it idempotent.
Test and refactor.

* Import modules, not names.
* Stricten port tests.
* Rename check_NAT_status to get_NAT_status.
* Test is_ipv6_address.
* Fix docstrings and test get_peer_url.