add test for virt-xml-validate

Signed-off-by: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>

virt_xml_validate: fix an spelling error in cfg and provide an interface for other schemas.

Signed-off-by: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>
Add test for virt-top.

Signed-off-by: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>

virt_top: remove an unused variable.

Signed-off-by: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>
Merge pull request #261 from yangdongsheng/virt_cmd_lxc

Add test for virt-top and virt-xml-validate. (qemu & lxc)
Modify get_disk_attr function according to PR#1780
Fix some bugs on rhel6.
Modify iscsi device creation method; delete usb tablet device before add it.
Modify operations on osxml according virt-test#1790.