ci: work around qemu hang

aux/qemu.py

+#!/usr/bin/python3
+# On recent kernels it seems -machine accel=kvm makes qemu hang with nested
+# kvm_amd. Thus wrap qemu and strip the parameter as needed.
+
+import os
+import sys
+
+args = sys.argv[:]
+
+# only strip -machine when actually booting, not for other operations e.g.
+# probing capabilities by libguestfs
+if '-machine' in args and '-append' in args:
+    idx = args.index('-machine')
+    del args[idx]
+    del args[idx]
+
+os.execve('/usr/bin/qemu-system-x86_64', args, os.environ)