When deploying devstack on a single host with a single NIC and
baremetal and neutron services enabled, the host looses Internet
access as default route is deleted.
Also, if localrc is not correctly set with correct values, OVS ports
and Neutron net and subnet aren't created (commands missing
arguments), we need devstack to properly fail.
Change-Id: I7f39bbdf7b8cb544b8b4a59effe16f04b85d1425