CI hotfix: Remove cpu passthrough

Some hypervisors really dislike cpu passthrough and it causes tests to fail.

test/image-tests/qcow2.sh

@@ -172,7 +172,6 @@ sudo virt-install \
     --import \
     --os-variant rhel8-unknown \
     --noautoconsole \
-    --cpu host-passthrough \
     --network network=default
 
 # Wait for the image to make a DHCP request.
@@ -233,4 +232,4 @@ else
   exit 1
 fi
 
-exit 0
+exit 0