Use config replace_on_change flag to decide whether to replace a deployment resource

As per the results of the following work session:
https://etherpad.openstack.org/p/heat-newton-sd-refinents

The inputs schema for the following config resources will gain a
'replace_on_change' boolean property:

- http://docs.openstack.org/developer/heat/template_guide/openstack.html#OS::Heat::SoftwareConfig-prop-inputs-*
- http://docs.openstack.org/developer/heat/template_guide/openstack.html#OS::Heat::SoftwareComponent-prop-inputs-*
- http://docs.openstack.org/developer/heat/template_guide/openstack.html#OS::Heat::StructuredConfig-prop-inputs-*

When a deployment resource has an input value which changes during a stack
update, it will trigger resource replacement if the input from the config has
replace_on_change:true.

When the config/deployment represents a self-contained scalable service (such
as a containerized service), replace_on_change can be used to bring up a new
service version before removing the old one.

An example usage would look something like this:

resources:
     backend_component:
       type: OS::Heat::SoftwareComponent
       update_policy: inputs_replacing: [DEPLOY_VERSION] #Option 3
       properties:
         configs:
           - tool: script
             actions:
               - CREATE
               - UPDATE
             config: |
               PORT=$(get_backend_port || random_port)
               stop_backend
               start_backend $DEPLOY_VERSION $PORT $CONFIG
               addr="$(hostname):$(get_backend_port)"
               printf '%s' "$addr" >${heat_outputs_path}.host_and_port
           - tool: script
             actions:
               - DELETE
             config: |
                stop_backend
          inputs:
            - name: DEPLOY_VERSION
              replace_on_change: true # backend resource will be replaced when this changes
            - name: CONFIG
          outputs:
            - name: host_and_port

     backend:
       type: OS::Heat::SoftwareDeployment
       properties:
         server: {get_resource: backend_server}
         name: {get_param: backend_version} # Forces upgrade replacement
         actions: [CREATE, UPDATE, DELETE]
         config: {get_resource: backend_component}
         input_values:
           DEPLOY_VERSION: {get_param: backend_version} # changing this will result in backend replacement
           CONFIG: {get_param: backend_config} # changing this will result in existing resource being updated in-place