For #772 we need to split Travis builds somehow so we don't run the basic linters twice.
In #758 there was a bad attempt as this lead to reinstalling packages multiple times.

Something like this split would probably make more sense:

• PYQT_INSTALLED=1 SYSTEM_SITE_PACKAGES=X
  • Installs Qt/PyQt/xvfb
  • Runs unittests, smoke, pylint and maybe pyflakes
• PYQT_INSTALLED=0
  • Doesn't install Qt/PyQt/xfvb
  • Runs misc, pep257, pep8, mccabe, pyroma, check-manifest and maybe pyflakes