This fix changes acceptance tests for VPN tunnel to use the correct ports (UDP
500 and 4500). It also changes the documentation to demonstrate using these
port single ports in a `port_range` field.
The GCE API for creating VPN tunnels began validating the `peerIp` field
and rejecting RFC5735 addresses. The previous test was using one of
these addresses and failing as a result. This commit uses 8.8.8.8
for the peerIp.
