Add dns_ptr_record_set resource

[jrandall]

Add a dns_ptr_record_set resource to manage PTR records as a set. With the existing dns_ptr_record, if there is an existing reverse DNS entry for an IP, terraform will add an additional one, and then get stuck not being able to work with the state because there are multiple PTR entries (it triggers the issue described in #93).

This adds a dns_ptr_record_set resource type as suggested by @bodgit in #93 (comment)

With this fix, setting the ptr record to a single element list will mean that terraform will remove any other extant entries and ensure that the listed entry is the only PTR record for the IP.

Theoretically, if someone wanted to manage multiple PTR records, this should also work for that -- I am not aware of a valid use-case for that, but since there are several DNS servers including the popular bind that allows that, it makes sense to manage the PTR records as a set.

Fixes #93

[hashicorp-cla]

All committers have signed the CLA.

[verejoel]

Will there be any movement on this? Would be useful for me to get this added.

[jrandall]

Apologies, I am working on getting permission to sign the CLA now.

[jrandall]

@hashicorp-cla my employer would prefer to sign a corporate CLA rather than have me sign on their behalf (as they would need to authorise me to do that).

This possibility is mentioned in CLA clause 4:
"... or that your employer has executed a separate Corporate CLA with HashiCorp"

How can we go about executing a corporate CLA?

I see this has been asked (but no apparent answer is visible) elsewhere: https://discuss.hashicorp.com/t/corporate-cla-info/11397

[bookshelfdave]

@jrandall if you email me at dave.parfitt at hashicorp dot com, I can help with the corporate CLA.

[p3kx]

Hello,
what is the current status?

I'm looking forward to this resource as well.