ResourceGroup doesn't work when there is no properties

[Thomas Herve]

When trying to create a ResourceGroup of a resource without properties, we get a failure "StackValidationFailed: 'NoneType' object is not iterable". Presumably the default value for properties is incorrect.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/79959

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/79959
Committed: https://git.openstack.org/cgit/openstack/heat/commit/?id=73c29d3edc41c2aafa7fc34d46c9e801bc13bd63
Submitter: Jenkins
Branch: master

commit 73c29d3edc41c2aafa7fc34d46c9e801bc13bd63
Author: Thomas Herve <email address hidden>
Date: Wed Mar 12 15:46:15 2014 +0100

    Default properties to the empty dict in ResourceGroup

    Sets the properties of the grouped resource to {} when it's None to make
    sure the resource is built properly.

    Change-Id: I2938c741063159ef81a7996d203adaf466cf19c4
    Closes-Bug: #1291421