* ability to pass port as a parameter
* try to find free ports
* use environment variables to pass mock server address
* get mock server address from environment variables
* ability to select ports for proxy in runtime
* use common method for URLs from mock server
* https support
* get mock server address
* get mock address
* replace hand-written mechanism by kernel-based one
* use ephemeral ports in mockserver
* strip EOL from addresses
* use ephemeral port in proxy
* no need to restore environment as it is restored in tearDown
* decode bytes
* use mockserver address as a variable
* ability to pass address as variable
* per test-case mockserver
* use base class
* remove obsolete environment manipulation
* return usage of proxy for http cases
* common method for broking proxy auth credentials
* python version-independent url methods
This allows to remove `get_testlog` helper, `flushLoggedErrors` from
twisted.trial.unittest.TestCase and Twisted log observers created for
each test on conftest.py.
