nixos/test-driver: allow overriding qemu binary in create_startcommand

nixos/lib/test-driver/test-driver.py

@@ -292,7 +292,12 @@ class Machine:
             net_frontend += "," + args["netFrontendArgs"]
 
         start_command = (
-            "qemu-kvm -m 384 " + net_backend + " " + net_frontend + " $QEMU_OPTS "
+            args.get("qemuBinary", "qemu-kvm")
+            + " -m 384 "
+            + net_backend
+            + " "
+            + net_frontend
+            + " $QEMU_OPTS "
         )
 
         if "hda" in args: