Added unit tests for websocket and websocketproxy

To run the unit tests just run tox from the top
level directory which will try to run unit tests
for most versions of python. Requires tox to be
installed. To run tox for a specifice env, run
tox -e<env> e.g. for python 2.7 run 'tox -epy27'.

Co-authored-by: natsume.takashi@lab.ntt.co.jp