bin/openquake and engine.py: Associate the current user with a calculation and outputs

[Lars Butler]

[et=6h]
[at=1.5h]

Currently, there is 1 user in the database (in the oq_user table): 'openquake'

- When a calculation is run, get the current username (using getpass.getuser(): http://docs.python.org/library/getpass.html#getpass.getuser)
- If the user does not exist, create an oq_user record for that username
- If it already exists, great; do nothing
- Get the OqUser Django model object for the user record
- This is user should be the owner all subsequent oq_job_profile, oq_calculation, and output records.

The reason why we want to do this is so that results displayed by the openquake command line interface are filtered by 'owner'.

[Lars Butler (lars-butler)]

Pull request: https://github.com/gem/openquake/pull/690