Default DNS server from config not used during deployment

[Victor Ryzhenkin]

HOW TO REPRODUCE:

1. Set in murano.conf default_dns = 8.8.8.8
2. Deploy environment with apache

Actual result:
Apache not installed because of
W: Failed to fetch http://http.debian.net/debian/dists/jessie/InRelease

This happened because of default_dns from config doesn't passthrough into environment model.

Environment properties:
'properties': {'ip_version': 4, 'cidr': u'10.0.1.0/24', 'dns_nameservers': [], 'network': {'get_resource': u'network-ea826385e3cd4019a41e015cebed1793'}}

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/211348

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/211348
Committed: https://git.openstack.org/cgit/openstack/murano/commit/?id=9026a8ff825404f160b3a0f50d01da60f29c7fd8
Submitter: Jenkins
Branch: master

commit 9026a8ff825404f160b3a0f50d01da60f29c7fd8
Author: Stan Lagun <email address hidden>
Date: Tue Aug 11 01:49:16 2015 +0300

    default_dns from config was never used

    NeutronNetwork class was comparing $.dnsNameservers to
    null and only then using config parameters. However property
    with list contract cannot be null as null (or missing) value will be
    converted to empty list

    Change-Id: Icc920e8979005446faf5c69eb9f22a1e8b7f054e
    Closes-Bug: #1483428