Updated openstack/openstack
Project: openstack-dev/devstack  8dab39854567df373233751be86871222e74aa06

Fix path to network interfaces configurations

This commit changes the path that is used as reference in the
documentation to one that is widely used in both ubuntu and debian. This
was made in order to avoid confusions (that actually happened while I
was trying out the devstack guide).

Change-Id: Ic3ce40816f79f9f522fc33ed8b4a574d7a57d586