colorizer: use staticmethod rather than classmethod
colorizer: use staticmethod rather than classmethod

The methods are actually not class methods at all as they do not use the
class nor the instance.

Change-Id: I04721bcaef30da291389a1144bdcfe65f10753b2

dims/glance,redhat-openstack/glance,openstack/glance,sigmavirus24/glance,takeshineshiro/glance,darren-wang/gl,jumpstarter-io/glance,saeki-masaki/glance,redhat-openstack/glance,darren-wang/gl,JioCloud/glance,tanglei528/glance,vuntz/glance,stevelle/glance,openstack/glance,jumpstarter-io/glance,paramite/glance,takeshineshiro/glance,wkoathp/glance,wkoathp/glance,ozamiatin/glance,akash1808/glance,saeki-masaki/glance,sigmavirus24/glance,JioCloud/glance,kfwang/Glance-OVA-OVF,scripnichenko/glance,kfwang/Glance-OVA-OVF,scripnichenko/glance,vuntz/glance,ozamiatin/glance,klmitch/glance,klmitch/glance,paramite/glance,rajalokan/glance,openstack/glance,stevelle/glance,akash1808/glance,rajalokan/glance,dims/glance,tanglei528/glance