Re-open packer/issues/10227 to address issue with defaulting to IPv6

[sier]

The issue with Packer attempting to use IPv6 is still an issue with the Proxmox provisioner (and I can only assume others as well).
The original issue has been closed without the second pull request to address this issue.
I wouldn't be opposed to having a switch option like "vm_interface_onlyipv4" for those masochists that have already adopted IPv6.

So far the only solution I can think of is to disable IPv6 completely, which isn't... ideal.

Original issue:

The problem is 2-fold.
The used API client for Proxmox (Telmate/proxmox-api-go) cannot parse IPv6 addresses with a zone id (delimited by "%").
I've wrote a simple fix which splits the IPv6 address at the delimiter "%" and returns the first part.
That fix can be checked here: Telmate/proxmox-api-go#112
Secondly I've added an extra check in the proxmox builder.go which basically tries to parse all IP addresses to IPv4 and thus returns the first valid IPv4 address.
I'll make the pull request.

Originally posted by @mmassez in hashicorp/packer#10227 (comment)