Use hiera lookup function with feature toggle to merge resource hashes.

[archii]

Addresses issue #614 - Hiera merge with multiple yaml files.

I've included a toggle parameter, $hiera_merge, to optionally enable this feature. This parameter defaults to false for backwards compatibility.

[wyardley]

Just wondering, since the Hiera v5 allows controlling the merge behavior more directly, is this still needed as a feature?
https://docs.puppet.com/puppet/5.1/hiera_merging.html#configuring-merge-behavior-in-hiera-data

[archii]

lookup_options does seem to make this feature unnecessary. I'll close this PR.

Should issue #614 be closed with a relevant comment?

Thanks.

[wyardley]

@archii I'll close it. If you notice @igalic's comments there, it's still probably worth converting to lookup(), now that the module is P4 only, welcome to submit a PR for those changes if you'd like.