Add Python 3 to CI build matrix

- Add Python 3.4 to CI build matrix so that we can see what would need to
  change to allow support for Python 3.
- Set build matrix to allow failures for Python 2.7 and 3.4 as they do not
  need to be supported at the moment.
- Set CI file to fast finish so we don't have to wait for builds of
  versions that are allowed to fail.

See "Details" in merge box for example.