Add testing for websocket server (WIP: Do not merge)

[yciabaud]

This PR attempts to add the websocket tracker to the test suite.
It is based on my scrape implementation (PR #125) because it is one required in the existing test case and the addition of the wrtc package (sorry about that).

I improved the closing of the websocket tracker in the client to prevent hanging at the end of the case but there are still 2 sockets running and I cannot get rid of it.

I believe the remaining socket are between the peers (because it does not happens for one peer) but I can achieve to find it.

I use the command wtfnode test/server.js to show the opened resources after the end of the test and I shows:

ok 100 should be equal
^C[WTF Node?] open handles:
- Sockets:
  - undefined:undefined -> undefined:undefined
    - Listeners:
  - undefined:undefined -> undefined:undefined
    - Listeners:

1..100
# tests 100
# pass  100

# ok

I leave this PR to get some help from you.
Any though?