vm: include /proc/xen in fstab (#466)

misc/fstab

@@ -13,4 +13,5 @@ tmpfs                   /dev/shm                tmpfs   defaults        0 0
 devpts                  /dev/pts                devpts  gid=5,mode=620  0 0
 sysfs                   /sys                    sysfs   defaults        0 0
 proc                    /proc                   proc    defaults        0 0
+xen                     /proc/xen               xenfs   defaults        0 0
 /dev/xvdi	/mnt/removable	auto noauto,user,rw 0 0