Add support for message cancellation to yggctl #171
Description
Now that message cancellation is possible through the D-Bus API, it would be useful to be able to cancel a message through yggctl. The public D-Bus API needs to add support for it as well. https://github.com/RedHatInsights/yggdrasil/blob/e5ae5b01493b0daf874bc45e2b389ad29ddf3909/dbus/com.redhat.Yggdrasil1.xml