Move resize_available class variable into skip decorators

We shouldn't do a getattr on CONF in the class definition. It will cause
import errors if there isn't a config file. Just use
CONF.compute_feature_enabled.resize in the skip decorator.

Change-Id: I6361ceb45b1e2796e00bb94279b5437c8902294d
Merge "Move resize_available class variable into skip decorators"