Update dependencies to latest stable versions

[Kami]

This pull request updates various dependencies to latest stable versions.

[Kami]

I also needed to push quite a lot of lint changes.

New version of flake8 adds some new checks, most important one being how regular expression strings are handled.

Now all the regular expression strings which contain special characters (\) need to be prefixed with r so they are treated as raw strings (so Python won't try to interpolate unicode escape sequences in the string and similar).

That was already a good practice before that check was added so it's a good change.

[Kami]

Need more workarounds for what looks like Travis caching and pip weirdness.

[bigmstone]

:(

[arm4b]

BTW related to that, I got this on local dev env unable to build from sources on a clean Ubuntu Xenial VM:

Generating requirements.txt for contrib/runners/action_chain_runner
===========================================================
Requirements written to: contrib/runners/action_chain_runner/requirements.txt
# Fix for Travis CI race
virtualenv/bin/pip install "six==1.11.0"
Requirement already satisfied: six==1.11.0 in ./virtualenv/lib/python2.7/site-packages
You are using pip version 9.0.3, however version 18.1 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.
# Fix for Travis CI caching issue
virtualenv/bin/pip uninstall -y "pytz"
Uninstalling pytz-2018.7:
  Successfully uninstalled pytz-2018.7
Traceback (most recent call last):
  File "virtualenv/bin/pip", line 11, in <module>
    sys.exit(main())
  File "/st2/virtualenv/local/lib/python2.7/site-packages/pip/__init__.py", line 248, in main
    return command.main(cmd_args)
  File "/st2/virtualenv/local/lib/python2.7/site-packages/pip/basecommand.py", line 252, in main
    pip_version_check(session)
  File "/st2/virtualenv/local/lib/python2.7/site-packages/pip/utils/outdated.py", line 102, in pip_version_check
    installed_version = get_installed_version("pip")
  File "/st2/virtualenv/local/lib/python2.7/site-packages/pip/utils/__init__.py", line 838, in get_installed_version
    working_set = pkg_resources.WorkingSet()
  File "/st2/virtualenv/local/lib/python2.7/site-packages/pip/_vendor/pkg_resources/__init__.py", line 644, in __init__
    self.add_entry(entry)
  File "/st2/virtualenv/local/lib/python2.7/site-packages/pip/_vendor/pkg_resources/__init__.py", line 700, in add_entry
    for dist in find_distributions(entry, True):
  File "/st2/virtualenv/local/lib/python2.7/site-packages/pip/_vendor/pkg_resources/__init__.py", line 1949, in find_eggs_in_zip
    if metadata.has_metadata('PKG-INFO'):
  File "/st2/virtualenv/local/lib/python2.7/site-packages/pip/_vendor/pkg_resources/__init__.py", line 1463, in has_metadata
    return self.egg_info and self._has(self._fn(self.egg_info, name))
  File "/st2/virtualenv/local/lib/python2.7/site-packages/pip/_vendor/pkg_resources/__init__.py", line 1823, in _has
    return zip_path in self.zipinfo or zip_path in self._index()
  File "/st2/virtualenv/local/lib/python2.7/site-packages/pip/_vendor/pkg_resources/__init__.py", line 1703, in zipinfo
    return self._zip_manifests.load(self.loader.archive)
  File "/st2/virtualenv/local/lib/python2.7/site-packages/pip/_vendor/pkg_resources/__init__.py", line 1643, in load
    mtime = os.stat(path).st_mtime
OSError: [Errno 2] No such file or directory: '/st2/virtualenv/local/lib/python2.7/site-packages/pytz-2018.7-py2.7.egg'
Makefile:363: recipe for target 'requirements' failed
make: *** [requirements] Error 1

[Kami]

I had similar issues here, even if I used old version of pytz. Looks like some pip related weirdness.

I got it to work by manually uninstalling python-dateutil and pytz once make requirements failed and then ran it again.

[Kami]

Just tested it again with a fresh vm and a new virtualenv and it seems to work fine.

[bigmstone]

:(