Property methods for resource metadata
Property methods for resource metadata

For OS::Nova::Server which will build its metadata dynamically
based on currently available SoftwareDeployment resources.
This change makes it possible to:
* read and assign resource.metadata as before
* subclassses to override resource.metadata for building dynamically
* allowing access to the simple attribute based resource._metadata
  when necessary

partial blueprint: hot-software-config
Change-Id: Ifd7aa15dd58c96e6b9efafe6b4201a964e140d8d

srznew/heat,maestro-hybrid-cloud/heat,pshchelo/heat,noironetworks/heat,miguelgrinberg/heat,cwolferh/heat-scratch,srznew/heat,dims/heat,jasondunsmore/heat,rdo-management/heat,gonzolino/heat,jasondunsmore/heat,dragorosson/heat,openstack/heat,NeCTAR-RC/heat,takeshineshiro/heat,pshchelo/heat,openstack/heat,cwolferh/heat-scratch,miguelgrinberg/heat,rdo-management/heat,rh-s/heat,ntt-sic/heat,steveb/heat,redhat-openstack/heat,takeshineshiro/heat,pratikmallya/heat,ntt-sic/heat,steveb/heat,rh-s/heat,cryptickp/heat,noironetworks/heat,cryptickp/heat,dims/heat,gonzolino/heat,NeCTAR-RC/heat,pratikmallya/heat,redhat-openstack/heat,maestro-hybrid-cloud/heat,dragorosson/heat