Add dependency `python-setuptools`

If setuptools is not installed, cthulhu cannot be started:
==============
# supervisorctl restart cthulhu
Traceback (most recent call last):
  File "/usr/bin/supervisorctl", line 5, in <module>
    from pkg_resources import load_entry_point
ImportError: No module named pkg_resources
Merge pull request #211 from cannium/master

Add dependency `python-setuptools`