Ok the term "Master" and "Slave" are master as running production VM and slave as backup vm for vMotion. So when running vm dies or lost connection, it gets automatically migrated to that "slave" vm which is not in production and using very little bit of resource. So it is just active-standby situation to clarify.
So, again, you're misunderstanding how vMotion works. A "backup VM for vMotion" doesn't/can't work because vMotion isn't a reaction to a failure (however you determine that) of a VM. That's what either vSphere HA does or some mechanism at the application layer does. I don't know what this application you have is, but what you need to look into is an application-level high availability solution because vMotion won't help you there.