Allow tcp_router.router_group to be overridden by spiff template
Allow tcp_router.router_group to be overridden by spiff template

- 'default-tcp' is also set as a default value in the spiff template if a property is not provided
- this property will be used by later bumps in cf-tcp-router but should not have an affect at this moment

[#142105731]

Signed-off-by: Charles Hansen <c376c0f4afe7933d7fe8f7dfb7f868092051f165@pivotal.io>

cloudfoundry-incubator/cf-routing-release,cloudfoundry-incubator/cf-routing-release,cloudfoundry-incubator/cf-routing-release