xenapi: Cleanup networking

OpenStack VM had 4 interfaces, from which eth0 was connected to HIMN (Host
Internal Management Network), and not used at all. The reason for not
using this interface according to johngarbutt is:
 - VNC console would not work
 - migrations would not work
 - many other things
This change removes the interface, thus devstack is providing the
same architecture as described in the official documentation, YAGNI
applied on the HIMN:

    http://goo.gl/dmrNF

The change also modifies some defaults, so it's easier to get started:
 - The Ubuntu VM is network-installed through the management network
 - OS VM is getting its address on the management network through DHCP
 - Default Public IP addresses aligned to stack.sh defaults
 - OS Services are listening on Management Interface

Related to blueprint xenapi-devstack-cleanup

Change-Id: I73c9751ade6f4786b8b682a1994cb87f0a624379
diff --git a/lib/nova b/lib/nova
index cac6330..afc540e 100644
--- a/lib/nova
+++ b/lib/nova
@@ -77,7 +77,7 @@
 
 # Set defaults according to the virt driver
 if [ "$VIRT_DRIVER" = 'xenserver' ]; then
-    PUBLIC_INTERFACE_DEFAULT=eth3
+    PUBLIC_INTERFACE_DEFAULT=eth2
     GUEST_INTERFACE_DEFAULT=eth1
     # Allow ``build_domU.sh`` to specify the flat network bridge via kernel args
     FLAT_NETWORK_BRIDGE_DEFAULT=$(sed -e 's/.* flat_network_bridge=\([[:alnum:]]*\).*$/\1/g' /proc/cmdline)