virttest.libvirt_xml: Fix wrong comment of vm_xml.set_cpu_mode.

Signed-off-by: Yu Mingfei <yumingfei@cn.fujitsu.com>
virttest.libvirt_xml: Add get_first_mac_by_name method for VMXML class.

Signed-off-by: Yu Mingfei <yumingfei@cn.fujitsu.com>
virttest.utils_libguestfs: Add functions for libguestfs tools.

Signed-off-by: Yu Mingfei <yumingfei@cn.fujitsu.com>
libguestfs.testcases: Add test for guestfish disk operations.

Signed-off-by: Yu Mingfei <yumingfei@cn.fujitsu.com>
Merge pull request #629 from yumingfei/guestfs_disk_oper

Libguestfs: Guestfs with disk operations