PEP8 compliance for model/cluster.py
PEP8 compliance for model/cluster.py

While checking my changes for pep8 compliance I noticed a few other
easily fixable cleanups.

Reviewed-By: Wesley Hertlein <ca32100e9f664971b15d1470ddc7f009d907efd3@morganstanley.com>

stdweird/aquilon,quattor/aquilon,guillaume-philippon/aquilon,guillaume-philippon/aquilon,guillaume-philippon/aquilon,stdweird/aquilon,stdweird/aquilon,quattor/aquilon,quattor/aquilon