Update Windows 7 scripts to use WinRM

[qmfrederik]

What this PR does

This PR updates the windows 7 scripts and updates them so that they use WinRM instead of SSH (which was broken, because the win-updates.ps script doesn't install SSH anymore).

It brings the script more in line with other Windows versions

Fixes include

• Setting the local to en-US instead of de-DE
• Use enable-winrm.ps1/win-updates.ps1 to enable WinRM instead of individual steps in Autounattended.xml
• Change the provisioner from shell to windows-shell.

I have validated this using qemu/KVM (the first commit includes the qemu-related changes, the second commit undoes them, you'll want to squash merge).

Why this PR is needed

We use Vagrant boxes for CI testing of our software. Windows 7 is still a supported (and massively used) baseline, so we're looking for a recent Vagrant box which includes Windows 7.

Unfortunately, the most popular Windows 7 boxes on Vagrant Atlas are all 4 to 5 years old. So we're looking for a new base box we can use.

[StefanScherer]

LGTM Thanks for updating the template!