hiera_data private_interface and data mapping

[Ken Schroeder]

Would be helpful to update the verbiage in section below for hiera_data/user.common.yaml

# The interface used for VM networking connectivity. This will usually
# be set to the same interface as public_interface.
private_interface: eth1

In data_mappings/enable_ha/true.yaml
private_interface:
  - openstack-ha::load-balancer::controller_interface

So private_interface variable is also used by load balancer modules. This has confused me in the past and got me again taking me bit of time to debug.