Ray.jl driver validates Raylet version is compatible

[omus]

The ray project is setup as a monorepo. This setup ensures that language and backend support are in lock step. With Ray.jl being a separate repo from the ray project we should utilize a runtime check to ensure that the backend the Ray.jl driver is connecting to is a version of ray that Ray.jl can work with.

As we currently use a custom fork of ray this check is a little more difficult to pull off unless we have some kind of feature query setup.

[omus]

Related changes to querying the raylet for information about itself: #202