pygrub: correct typo in --args assignment

If pygrub was called with --args="some thing", then this string should
be append to the kernel command line.  But the last changeset
25941:795c493fe561 contained a typo, it assigns 'args' instead of 'arg'.

Rename the local variable which holds the string from the domain config
file to avoid further confusion.

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Committed-by: Ian Campbell <ian.campbell@citrix.com>

xen-unstable changeset: 26018:ecc7627ca6d7
Backport-requested-by: Ian Campbell <Ian.Campbell@citrix.com>
Committed-by: Ian Jackson <ian.jackson@eu.citrix.com>

tools/pygrub/src/pygrub

@@ -585,7 +585,7 @@ def get_entry_idx(cf, entry):
 
     return None
 
-def run_grub(file, entry, fs, arg):
+def run_grub(file, entry, fs, cfg_args):
     global g
     global sel
 
@@ -622,8 +622,8 @@ def run_grub(file, entry, fs, arg):
         grubcfg["ramdisk"] = img.initrd[1]
     if img.args:
         grubcfg["args"] += img.args
-    if arg:
-        grubcfg["args"] += " " + args
+    if cfg_args:
+        grubcfg["args"] += " " + cfg_args
 
     return grubcfg