xend: fix insufficient quoting in tapdisk

Fix insufficient quoting between "tap-ctl list" and
xend/server/BlktapController.py

The "line.split(None, 4)" needs to be a "3", because 3 splits needs to
be done to get the 4 parts.  Sorry for the mixup.

[ fix to 24335:3915bd95ade5. -iwj ]

Committed-by: Ian Jackson <ian.jackson@eu.citrix.com>

tools/python/xen/xend/server/BlktapController.py

@@ -253,7 +253,7 @@ class TapdiskController(object):
             tapdisk = TapdiskController.Tapdisk()
 
             # Since 'tap-ctl list' does not escape blanks in the path, hard-code the current format using 4 pairs to prevent splitting the path
-            for pair in line.split(None, 4):
+            for pair in line.split(None, 3):
                 key, value = pair.split('=', 1)
                 if key == 'pid':
                     tapdisk.pid = value