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, This change is causing error in several test cases like
`virsh.vol_clone_wipe.positive_test.non_acl.vol_format.raw_f.pool_type.dir`
`virsh.vol_download_upload.download_upload.dir_pool.download.non_acl.0-1024`.
In there cases the pool is create as a transient pool using `virsh pool-create-as`,
so undefine it anyway will eventually return False. Please help correct this, thanks.