[policyguidedful] ignore None in mapping

[Radek Pospisil]

In some cases None value is mapped as empty string"". To be aligned with murano congress driver it must not be mapped.

json:
015-02-19 11:19:26.285 13013 DEBUG murano.policy.model_policy_enforcer [-] {'defaultNetworks': {'environment': '?': {id: 33ac683a667a49cb8124a15c4037430c, type: io.murano.resources.NeutronNetwork}
autoUplink: true
autogenerateSubnet: true
dnsNameserver: null
externalRouterId: null
name: hello-network
subnetCidr: null
useDefaultDns: true
, 'flat': None}, 'name': u'hello', '?': {'type': u'io.murano.Environment', 'id': u'688493b877d24f768fa222a9ecce6e4a'}, 'applications': ['?': {id: 9e8505a4-ca6a-4887-b57b-ca12ef6fad51, type: io.murano.data
database: ''

mapping:
  murano:properties+("688493b877d24f768fa222a9ecce6e4a", "defaultNetworks.flat", "")

->

not-mapped :-)

[Serg Melikyan (smelikyan)]

Fixed in https://review.openstack.org/159849