moving rabbitMq host to resolved value

[jeffhollan]

resolve #89

Making a WIP PR as there is a big question on how we release this as it will be breaking.

[jeffhollan]

Actually one thought here that may add consistency and make non-breaking too.

Potentially we can add a new property called connection that resolves from Env. For the time being we could support both (host as a literal value, connection as a resolved value). Before we 1.0 we would remove support for host and only accept connection. This would also make naming more in line with other scalers.

[tomkerkhove]

@jeffhollan Given this is still in "alpha"/"beta" and we have the auth changes coming up, I would just consider it as breaking change.

We've discussed this as well for the auth changes and would suggest to introduce a versioned image tag which contains the new features for more stable images

[jeffhollan]

Ok great - yeah let's just do as-is and change how host behaves. @ahmelsayed is going to take a snapshot version of current keda:latest so that people can easily roll back to it as needed if they break from this PR, and the many more around auth spec that will start rolling out

[ahmelsayed]

Thanks @jeffhollan :)

[ahmelsayed]

btw, kedacore/keda:0.2 is the snapshot. I updated :latest to :master right before this merge. Will update it again to include this once the build is done on dockerhub.