virttest.storage: fix type convert error

conver host_set_flag  param to int before operation.

Signed-off-by: Xu Tian <xutian@redhat.com>
thanks your comment, updated it.

On 12/04/2014 09:58 AM, Fergus Yu wrote:
>
> In virttest/storage.py:
>
> > @@ -429,7 +429,7 @@ def __init__(self, params, root_dir, tag):
> >          :param root_dir: Base directory for relative filenames.
> >          :param tag: Image tag defined in parameter images
> >          """
> > -        host_set_flag = params.get("host_setup_flag")
> > +        host_set_flag = int(params.get("host_setup_flag", 0))
> >          if host_set_flag is not None:
>
> But host_set_flag will never be None...Shouldn't it be updated too?
>
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> <https://github.com/autotest/virt-test/pull/1906/files#r21281393>.
>