qemu_cpu.cfg: set auto_cpu_model = no

Without this option, autotest will set a "cpu_model" config option by
itself.
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>

qemu/tests/cfg/qemu_cpu.cfg

@@ -3,6 +3,10 @@
     type = cpuid
     start_vm = "no"
     smp = 1
+
+    # ask autotest to not mess with the cpu_model settings
+    auto_cpu_model = no
+
     # QEMU versions:
     variants:
         - unknown_qemu: