Use hiera_hash(...) instead of hiera(...) so that matches throughout the Hiera hierarchy can be merged

Using `hiera(...)` to retrieve config settings prevents [hierarchies](https://docs.puppetlabs.com/hiera/1/hierarchy.html) from being merged correctly. `hiera_hash(...)` is required for the merges to take place properly (see [Hiera Hash](https://docs.puppetlabs.com/references/latest/function.html#hierahash) and [Hiera Lookup Functions](https://docs.puppetlabs.com/hiera/1/puppet.html#hiera-lookup-functions))

This PR changes all instances of `hiera(...)` to `hiera_hash(...)`.

**Note:** `hiera_hash(...)` expects the top-level value in the hierarchy to be a hash, but this should be backwards compatible because all affected configurations are hashes.