keep variant setting removed by previous commit

to avoid error like:
===
$~/createhdds/createhdds.py  support
...
Traceback (most recent call last):
  File "/root/createhdds/createhdds.py", line 821, in <module>
    main()
  File "/root/createhdds/createhdds.py", line 811, in main
    args.func(args, hdds)
  File "/root/createhdds/createhdds.py", line 701, in cli_image
    img.create(args.textinst)
  File "/root/createhdds/createhdds.py", line 291, in create
    loctmp.format(fedoradir, str(self.release), variant, arch), "--name", "createhdds",
NameError: name 'variant' is not defined
===

Signed-off-by: Michel Normand <normand@linux.vnet.ibm.com>

createhdds.py

@@ -269,6 +269,8 @@ class VirtInstallImage(object):
             # from F26 onwards, i686 is in fedora-secondary
             fedoradir = 'fedora-secondary'
 
+        variant = self.variant
+
         try:
             # this is almost complex enough to need fedfind but not
             # quite, I think. also fedfind can't find the 'transient'