tools: fix shared loop device detection in block hotplug script

We need to cope with 0 or more '0' prefixed to '$dev':

  # stat -c '%D' "/system.img"
  13
  # losetup -a
  /dev/loop0: [0013]:12062248 (/system.img)

Signed-off-by: Zhigang Wang <zhigang.x.wang@oracle.com>
Committed-by: Ian Jackson <ian.jackson@eu.citrix.com>

tools/hotplug/Linux/block

@@ -280,7 +280,7 @@ mount it read-write in a guest domain."
           fi
 
           shared_list=$(losetup -a |
-                sed -n -e "s@^\([^:]\+\)\(:[[:blank:]]\[${dev}\]:${inode}[[:blank:]](.*)\)@\1@p" )
+                sed -n -e "s@^\([^:]\+\)\(:[[:blank:]]\[0*${dev}\]:${inode}[[:blank:]](.*)\)@\1@p" )
           for dev in $shared_list
           do
             if [ -n "$dev" ]