xend: Tidy bootloader device constant.

In XendDomainInfo, BOOTLOADER_LOOPBACK_DEVICE is defined to be
'/dev/xvdp'.  However, there is still one place in this file that has
'/dev/xvdp' hard-coded.

Signed-off-by: Charles Coffing <ccoffing@novell.com>

tools/python/xen/xend/XendDomainInfo.py

@@ -1820,7 +1820,7 @@ class XendDomainInfo:
                     log.info("Unmounting %s from %s." %
                              (fn, BOOTLOADER_LOOPBACK_DEVICE))
 
-                    dom0.destroyDevice('tap', '/dev/xvdp')
+                    dom0.destroyDevice('tap', BOOTLOADER_LOOPBACK_DEVICE)
 
             if blcfg is None:
                 msg = "Had a bootloader specified, but can't find disk"