Fix logging output directory

When main.py was moved into performanceplatform.collector the logging
path was not changed. This should expect and output to a directory in
the root of the project called log.
Call pp-collector rather than main.py

It is not polite to call down into nested packages when we expose a
named script you can run. This changes the outputted cronjobs to call
this script rather than main.py
Merge pull request #11 from alphagov/deployment-fixes

Deployment fixes