Fix the description of LVSB sub testset.

It seems a error from copy-paste, the description of LVSB sub tests
is "Libvirt subtests".

This patch change it to "LVSB subtests".

Signed-off-by: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>
Merge pull request #30 from yangdongsheng/MAINTAINER

Fix the description of LVSB sub testset.