xend: fix "xm block-detach 0 ..." for extended-ID devices

Simply taking stat()'s st_rdev doesn't work here, as the minor is
split into two parts, the major is present, and the "extended" bit
isn't set.

Rather than fixing this in a way that would likely be OS-dependent,
simply remove the access to the device file, and instead just parse
the provided string (as is done e.g. for block-attach).

Signed-off-by: Jan Beulich <jbeulich@novell.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>

tools/python/xen/util/blkif.py

@@ -19,11 +19,6 @@ def blkdev_name_to_number(name):
     devname = 'virtual-device'
     devnum = None
 
-    try:
-        return (devname, os.stat(n).st_rdev)
-    except Exception, ex:
-        pass
-
     scsi_major = [ 8, 65, 66, 67, 68, 69, 70, 71, 128, 129, 130, 131, 132, 133, 134, 135 ]
     if re.match( '/dev/sd[a-z]([1-9]|1[0-5])?$', n):
         major = scsi_major[(ord(n[7:8]) - ord('a')) / 16]