Description of problem:
Configuring a compute node with quickstack::neutron::compute with the "private_interface" set to an interface name without an IP address configured results in the following Puppet error:

Error: Could not retrieve catalog from remote server: Error 400 on
SERVER: value is a required option for Puppet::Parser::Resource::Param
on node example.redhat.com

Version-Release number of selected component (if applicable):
packstack-modules-puppet-2013.2.1-0.7.dev806.el6ost.noarch
openstack-foreman-installer-0.0.21-1.el6ost.noarch
puppet-3.2.4-1.el6_4.noarch

How reproducible:
Always

Steps to Reproduce:
1. Set up openstack-foreman with a private interface present but unconfigured on a compute node
2. Assign the OpenStack Neutron Compute host group to the node
3. Run puppet on the node

Actual results:
Error: Could not retrieve catalog from remote server: Error 400 on
SERVER: value is a required option for Puppet::Parser::Resource::Param
on node example.redhat.com

Expected results:
Error: Could not retrieve catalog from remote server: Local ip for ovs agent must be set when tunneling is enabled at <path to neutron/agents/ovs.pp>:28 on node example.redhat.com

(please ensure the manifest file + line number are present)

Additional info:
Caused by http://projects.puppetlabs.com/issues/23115

For example:
# /etc/puppet/node.rb example.comredhat.com | grep private_interface
    private_interface: p3p1

# egrep "interfaces|ipadd"
/var/lib/puppet/yaml/facts/example.redhat.com.yaml
    ipaddress: "10.16.139.12"
    interfaces: "em1,em2,em3,em4,lo,p3p1,p3p2"
    ipaddress_lo: "127.0.0.1"
    ipaddress_em1: "10.16.139.12"

The ipaddress_p3p1 fact is missing, so the interface must be present but unconfigured.

In /etc/puppet/environments/production/modules/quickstack/manifests/neutron/compute.pp:106:

  class { '::neutron::agents::ovs':
      bridge_uplinks   => $ovs_bridge_uplinks,
      bridge_mappings  => $ovs_bridge_mappings,
      local_ip         => getvar("ipaddress_${private_interface}"),
      enable_tunneling => true,
  }

The getvar() function evaluates to nil, but Puppet should treat this as undef, then it would pass undef through to the neutron::agents::ovs class, which would do this error checking:

  if $enable_tunneling and ! $local_ip {
    fail('Local ip for ovs agent must be set when tunneling is enabled')
  }

Instead we're hitting an internal Puppet bug where the param evaluates to nil.