This enforces our use of a consistent style in how we access Python
modules; "from os.path import dirname" is a particularly popular
abbreviation inconsistent with our style, and so it deserves a lint
rule.
Commit message and error text tweaked by tabbott.
Fixes#6543.
The manage.py change effectively switches the Zulip production server
to use the virtualenv, since all of our supervisord commands for the
various Python services go through manage.py.
Additionally, this migrates the production scripts and Nagios plugins
to use the virtualenv as well.
julianasobreira
Tim Abbott
Anders Kaseorg
Eklavya Sharma