V2V: Fix some problems

1.Default cases in tests.cfg is v2v_quick which contains only three tests.
   To list them all with run script, adding another v2v_all content.
2.For remote host, if its language is not en.US, pool_exists will return False.
   Then pool will be not undefined.So do some changes.
3.Options for virt-v2v have fixed network to "-n", now support "-b".
4.Add mk_label function for creating disk pool, because unlabelled disk can not be used for pool.
@yumingfei , I agree with this fix. BTW, I think the logging.error() should be moved down to `if` block since that should not be considered as an error. Thanks.