Update hackings jobs

* Make pypy voting again. It was disabled due to some issues, but
  it appears to be working again.
* Drop gate-hacking-integration-nova from gate, as the job is designed
  to be non-voting.
* Add python34 job as non-voting, as the first step in getting python34
  support.

Change-Id: Icaf5848eec8b30d77f4c5a8a21f7e6ca4ccc7924
Merge "Update hackings jobs"