Merge branch 'master' into v3_merge

Includes minor py3 fixes (for pep8 on py3).

 Conflicts:
	tests/base.py
	tests/test_model.py
	tests/test_scheduler.py
	tox.ini
	zuul/model.py
	zuul/reporter/__init__.py
	zuul/scheduler.py
	zuul/source/gerrit.py

Change-Id: I99daf9acd746767967b42396881a2dff82134a07