Fix translation issue with version 5 hiera.yaml

[logic]

With the version 5 hiera.yaml format, we can still use older custom backends like this via hiera3_backend. There appears to be some magic to translate hash keys from name to :name for compatibility purposes, but it doesn't appear to recurse down into options more than one level deep, resulting in a mounts hash that looks like "generic"=>"foo"} instead of :mounts=>{:generic=>"puppet"}. This is a quick hack to just work around the problem, in lieu of a proper conversion to version 5.