Ensure why-run of a FreeBSD service missing init script does not fail

On FreeBSD, a why-run including a service resource fails if the service's init script is missing. I think it makes sense to assume that the init script will be in place in an actual Chef run rather making the why-run fail.

The FreeBSD service provider has two assertions that expect the init script to be in place. Rather than have two assertions fail for the same reason, I've added a why-run message for the first while setting a default init script path to allow the second to pass.