Use the "iterate timeout" idiom from nodepool
Use the "iterate timeout" idiom from nodepool

When waiting for something to happen inside of a timeout loop,
use a generator to simplify and standardize the pattern.

Change-Id: I1a49bd4ecde98bc6bbb20d64d43447f825776807

openstack/python-openstacksdk,openstack-infra/shade,openstack-infra/shade,stackforge/python-openstacksdk,jsmartin/shade,dtroyer/python-openstacksdk,jsmartin/shade,dtroyer/python-openstacksdk,stackforge/python-openstacksdk,openstack/python-openstacksdk