Adds two config options to the Proxmox builder:
```
http_interface
vm_interface
```
Both give the user the ability to specify an interface whos IP will be set as the `.HTTPIP` and VMIP respectively.
This is useful when the VM and or the machine executing Packer has multiple interfaces.
Until now Packer would accept the first non-loopback IP as the `.HTTPIP` and VMIP.
I'm open to suggestions and any kind of feedback.
* Added ability to define the NIC where the HTTPIP is taken from.
* Added VM interface config option
* fmt and documentation
* Moved HTTPInterface into HTTPCommon
* Build Fix
* Documentation Fix
Andreas Botzner
Joshua Foster
Adrien Delorme
Matthew Hooker
Mark Peek