(RFE) Add ability to enable/disable Spanning Tree Protocol on OVS bridges using TripleO templates

Description
===========
There is currently no THT argument to enable / disable Spanning Tree in OvS. I'm raising this as an RFE to add the functionality to the default THTs.

Expected result
===============
Add an argument similar to:
SpanningTreeProtocol: {True,False}
SpanningTreeBridgeName: {br-int,br-ex,br-tun,etc}

Actual result
=============
Currently no argument exists.

Environment
===========
1. Train

Logs & Configs
==============

The functionality can be achieved with a Heat template similar to this one:

heat_template_version: 2014-10-16

description: >
  Enable or Disable Spanning Tree Protocol

parameters:
  servers:
    type: json
  stp_value:
    type: string
  bridge_value:
    type: string
  DeployIdentifier:
    type: string

resources:
  CustomExtraConfig:
    type: OS::Heat::SoftwareConfig
    properties:
      group: script
      config:
        str_replace:
          template: |
            #!/bin/sh
            sudo ovs-vsctl set bridge _BRIDGE_VALUE_ stp_enable=_STP_VALUE_
          params:
            _STP_VALUE_: {get_param: stp_value}
            _BRIDGE_VALUE_: {get_param: bridge_value}

  CustomExtraDeployments:
    type: OS::Heat::SoftwareDeploymentGroup
    properties:
      servers: {get_param: servers}
      config: {get_resource: CustomExtraConfig}
      actions: ['CREATE','UPDATE']
      input_values:
        deploy_identifier: {get_param: DeployIdentifier}

Env File:
resource_registry:
  OS::TripleO::NodeExtraConfigPost: /home/stack/stp-test.yaml

parameter_defaults:
  stp_value: "false"
  bridge_value: "br-int"