Fix processing of routes in init-neutron-ovs

The existing routes via the external network interface
are parsed incorrectly (routes are not split on new
lines), which makes init-neutron-ovs fail and leaves the
external bridge in partially configured state.

Closes-Bug: #1244188

Change-Id: Ifae4f24c7c08db0ab0f1885db604152ffa1d1a12