virttest.libvirt_storage: Fix a typo.

Signed-off-by: Yu Mingfei <yumingfei@cn.fujitsu.com>
utils_test.libvirt: Enhancements of setup/cleanup nfs/iscsi functions.

Signed-off-by: Yu Mingfei <yumingfei@cn.fujitsu.com>
Merge pull request #1474 from yumingfei/pool_enhancements

Storage relative enhancements