Docker support

Enable a docker based build.

allow image to be run standalone or through the command line
Make sure we build with right ssl header

Avoid :

````
Traceback (most recent call last):
  File "/redbot/bin/redbot", line 102, in <module>
    main()
  File "/redbot/bin/redbot", line 94, in main
    thor.run()
  File "build/bdist.linux-x86_64/egg/thor/loop.py", line 115, in run
  File "build/bdist.linux-x86_64/egg/thor/loop.py", line 333, in _run_fd_events
  File "build/bdist.linux-x86_64/egg/thor/loop.py", line 195, in _fd_event
  File "build/bdist.linux-x86_64/egg/thor/events.py", line 109, in emit
  File "build/bdist.linux-x86_64/egg/thor/tcp.py", line 152, in handle_read
  File "/usr/lib/python2.7/ssl.py", line 709, in recv
    return self.read(buflen)
  File "/usr/lib/python2.7/ssl.py", line 603, in read
    v = self._sslobj.read(len or 1024)
ssl.SSLWantReadError: The operation did not complete (read) (_ssl.c:1750)
````
Adding the tests to the build, cost in image size is not too bad

I'd add pylint, but it's currently failing.
Merge branch 'docker'