When using an old version of Foreman, say '1.10' against a newer version of the proxy, say one that contains the 'logs' feature, the /features call will return an array ['logs'].
If you try to add a smart-proxy that only has this feature, the check we make `reply.is_a?(Array) and reply.any?` is not enough. We should verify we have the features in the db.

Currently the problem is:

- I try to add new smart-proxy with features ['logs'] to old foreman without this feature.
- Submit, it won't save. But it won't throw any error either.

We should display an error and say 'the features in this proxy are not recognized by foreman'.