When deploying an Instance joined to ExistingNeutronNetwork its
ipAddresses property returned an empty list, which was causing most of
the applications to fail. This happened because the responsibility of
managing HOT outputs for the instance IP was moved to the Network
classes and was implemented for the NeutronNetwork but not the
ExistingNeutronNetwork.
This commit moves the logic to the base class for all Neutron networks
and refactors it so that it could be used for them all
Change-Id: I552098683e0faeb66f7c622ea8c1d073a82d6338
Closes-Bug: #1649715
6f787ab5a2