@achim71
Thank you for the hint. I first tried your changes but it did not work in Remote Upgrade mode (i did not use an extra answer file, I just used the same commands I posted above).
On second try I used these modifications and now it works!
https://github.com/xcp-ng/host-installer/commit/336b2b64fc0f8a6e113ca69dd3053b3124c34426#diff-6c480f72da7e1acb5eab3acf571a27e2
I unpacked the install.img, modified the script, repacked install.img and placed it on our web server.

@rj-dsl
My second test system is with X5670, but I also may have some other servers with E5520

EDIT: Remote Upgrade (with patch) worked on
Asrock FM2A88x Extreme4+ with AMD A8-6500
HP ML350 G6 with two Intel Xeon X5670

0 bdonnahue committed to xcp-ng/host-installer

[Bug fix] - Variable referenced before assignment (#11)

* [Bug fix] - Variable referenced before assignment

The installation will fail while using an answefile_generator script. The results variable is referenced before assignment.

Remote Upgrade from 7.6 to 8.0 RC1 does not seem to work currently (tried on two different hosts)

1. In dom0 shell:

• get UUID of host
  xe host-list
• Test
  xe host-call-plugin plugin=prepare_host_upgrade.py host-uuid=<uuid> fn=testUrl args:url=http://my.example.com/xs/releases/xcp-ng-8.0.0-rc1/
  (returns true)
• Prepare
  xe host-call-plugin plugin=prepare_host_upgrade.py host-uuid=<uuid> fn=main args:url=http://my.example.com/xs/releases/xcp-ng-8.0.0-rc1/
  (returns true)
• reboot

2. Server boots , Blue background shows up

3. Dialog
   Attempting to configure networking...

4. Dialog
   Error occured
   local variable 'results' referenced before assignment