fix: Clearer error messaging when VM generation detection goes wrong

[bdonaldson77]

When running a Packer build in a situation where you already have a HyperV VM with the same name as your desired build VM's name, you will receive a cryptic error when Packer attempts to determine the VM's generation to determine its capabilities:

2024-11-18T15:03:35-08:00: Build 'hyperv-vmcx' errored after 55 seconds 702 milliseconds: Error detecting vm generation: strconv.ParseUint: parsing "2\r\n2": invalid syntax

==> Wait completed after 55 seconds 702 milliseconds

==> Some builds didn't complete successfully and had errors:
--> hyperv-vmcx: Error detecting vm generation: strconv.ParseUint: parsing "2\r\n2": invalid syntax

By adding a check to compare the result of the script that detects the generation of the VM to a regex, it does not alter the functionality, but makes it much clearer that the error happened because the VM generation detection script returned an unexpected result.

2024-11-18T15:29:54-08:00: Build 'hyperv-vmcx' errored after 1 minute 5 seconds: Error detecting vm generation: PowerShell error: Unable to parse VM generation. Are there multiple VMs with the same name?

I initially looked at swallowing the error if the results of the generation check were all identical (e.g. if you have 3 VMs and all are generation 2, logically you could return that your VM is generation 2,) but that opens the door to problems later when other commands run against a given VM name and receive multiple results (e.g. powering on all the VMs instead of just the one you wanted.)