Includes a validation to disable creating initial networks for Neutron

Neutron external and internal networks are created by default
This commit let developers by configuration to decide if those
networks needs to be created. This is needed to test Neutron DVR
in a distributed Multi-node environment

Change-Id: I17d891d072f189925676b4557094cde1c7a71579
Closes-Bug: 1389288
Merge "Includes a validation to disable creating initial networks for Neutron"