libguestfs: Add 2 funcs for virt-command
1. Get virt-sysprep operation list
2. Check if option is supported by virt-command

Signed-off-by: Li Yang <liyang.fnst@cn.fujitsu.com>
libguesfs: Add virt-ls command function

Signed-off-by: Li Yang <liyang.fnst@cn.fujitsu.com>