Improve yaml output of "openstack overcloud node provision"
Improve yaml output of "openstack overcloud node provision"

The non-default flow style is better at spreading the yaml over
multiple lines, which is better for readability.

Change-Id: Ibb0c6fb927eca279724cd18e4f8fc9669c02e957
Blueprint: nova-less-deploy

openstack/python-tripleoclient