XenAPI: Get the management network dynamically

xenbr0 is correct for most installations, but not all.  Notable xenserver-core
may use a differently named device.  Since we can auto detect this, remove the
config and do so.

Change-Id: I989f6ddd5ffb526ab350f263ef6fc402c596304a
diff --git a/tools/xen/xenrc b/tools/xen/xenrc
index f698be1..82aa298 100644
--- a/tools/xen/xenrc
+++ b/tools/xen/xenrc
@@ -20,9 +20,7 @@
 # differ across localised versions of XenServer. If a given bridge/network
 # was not found, a new network will be created with the specified name.
 
-# The management network is specified by the bridge name. xenbr0 is usually
-# the name of the bridge of the network associated with the hypervisor's eth0.
-MGT_BRIDGE_OR_NET_NAME="xenbr0"
+# Get the management network from the XS installation
 VM_BRIDGE_OR_NET_NAME="OpenStack VM Network"
 PUB_BRIDGE_OR_NET_NAME="OpenStack Public Network"
 XEN_INT_BRIDGE_OR_NET_NAME="OpenStack VM Integration Network"
@@ -72,7 +70,6 @@
 UBUNTU_INST_LOCALE="en_US"
 UBUNTU_INST_KEYBOARD="us"
 # network configuration for ubuntu netinstall
-UBUNTU_INST_BRIDGE_OR_NET_NAME=${UBUNTU_INST_BRIDGE_OR_NET_NAME:-"$MGT_BRIDGE_OR_NET_NAME"}
 UBUNTU_INST_IP="dhcp"
 UBUNTU_INST_NAMESERVERS=""
 UBUNTU_INST_NETMASK=""