Add new XEN_BRIDGE variable.

This can be used to configure the bridge on which the helper's VM
nic will be attached when using XEN.

snf-image-host/common.sh.in

@@ -396,6 +396,7 @@ fi
 : ${PITHOS_DATA:="@localstatedir@/lib/pithos/data/"}
 : ${PROGRESS_MONITOR:="@PROGRESS_MONITOR@"}
 : ${UNATTEND:="@UNATTEND@"}
+: ${XEN_BRIDGE:="xenbr"}
 
 case $HYPERVISOR in
     xen-hvm|xen-pvm) . xen-common.sh ;;

snf-image-host/defaults

@@ -79,6 +79,9 @@
 # this empty.
 # UNATTEND=""
 
+# XEN_BRIDGE: Bridge to connect the helper VM on
+# XEN_BRIDGE=xenbr
+
 # Paths for needed programs. Uncommend and change the variables below if you
 # don't want to use the default one.
 # LOSETUP="losetup"

snf-image-host/xen-common.sh

@@ -17,7 +17,7 @@ launch_helper() {
       disk="file:$snapshot,xvda,w" \
       disk="phy:$blockdev,xvdb,w" \
       disk="file:$floppy,xvdc1,w" \
-      vif="mac=aa:00:00:00:00:11,bridge=xenbr" \
+      vif="mac=aa:00:00:00:00:11,bridge=$XEN_BRIDGE" \
       memory="256" root="/dev/xvda1 quiet ro boot=local" boot="c" vcpus=1 \
       name="$helper_name"