xenapi: cleanup VM Installation

VM installation created a machine with multiple network interfaces. This
is a needless complexity at that point, we only need one interface. This
change removes the complex network interface setup from
install-os-vpx.sh script, so that only one network interface is created,
which is connected to the selected network (management by default). This
change also removes a lot of non-used code from install-os-vpx.sh
Specify the network to be used for ubuntu netinstall with:

    UBUNTU_INST_BRIDGE_OR_NET_NAME

defaults to $MGT_BRIDGE_OR_NET_NAME.

This change also includes:
 - use precise as default

Related to blueprint xenapi-devstack-cleanup

Change-Id: Ib0a0a316e849f2c2651305ea657c84820cd2bb3b
diff --git a/tools/xen/install_os_domU.sh b/tools/xen/install_os_domU.sh
index be4aa16..63295d1 100755
--- a/tools/xen/install_os_domU.sh
+++ b/tools/xen/install_os_domU.sh
@@ -198,13 +198,11 @@
     # Update the template
     $THIS_DIR/scripts/install_ubuntu_template.sh $PRESEED_URL
 
-    # create a new VM with the given template
-    # creating the correct VIFs and metadata
+    # create a new VM from the given template with eth0 attached to the given
+    # network
     $THIS_DIR/scripts/install-os-vpx.sh \
         -t "$UBUNTU_INST_TEMPLATE_NAME" \
-        -v "$VM_BRIDGE_OR_NET_NAME" \
-        -m "$MGT_BRIDGE_OR_NET_NAME" \
-        -p "$PUB_BRIDGE_OR_NET_NAME" \
+        -n "$UBUNTU_INST_BRIDGE_OR_NET_NAME" \
         -l "$GUEST_NAME" \
         -r "$OSDOMU_MEM_MB"