libvirt-virsh: update vcpupin function.

Adapt this function to virsh-style, returning a CmdResult object.

Signed-off-by: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>
utils_test: Add two utils functions into utils_test.

Signed-off-by: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>
libvirt-tests: update virsh vcpupin test.

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