virttest.utils_misc: Update invalid syntax for python 2.4 in rhel5 host.

Signedble = 1 if enable else 0
  File "<stdin>", line 1
    cpu_enable = 1 if enable else 0
                    ^
SyntaxError: invalid syntax

-off-by: Feng Yang <fyang@redhat.com>
Signed-off-by: Feng Yang <fyang@redhat.com>
virttest.qemu_storage: Change the way used to check image_cluster_size set or not.

check image_cluster_size by:
 if image_cluster_size:
So image_cluster_size = will think as not set.

Signed-off-by: Feng Yang <fyang@redhat.com>
Merge pull request #1895 from FengYang/python2.4

Python2.4