Backport PRIVATE_NETWORK_NAME

Backports portions of https://review.openstack.org/14798 to set
PRIVATE_NETWORK_NAME in stackrc/localrc

Change-Id: I3478143847021c53790683eead118383184bb427
Add PUBLIC_NETWORK_NAME

Change-Id: Idf701fbb775383593f1fba15a2b6049161c120c3