tests/acceptance: Handle cpu tag on x86_cpu_model_versions tests

tests/acceptance: Handle cpu tag on x86_cpu_model_versions tests

Some test cases on x86_cpu_model_versions.py are corner cases because they
need to pass extra options to the -cpu argument. Once the avocado_qemu
framework will set -cpu automatically, the value should be reset. This changed
those tests so to call set_vm_arg() to overwrite the -cpu value.

Signed-off-by: Wainer dos Santos Moschetta <wainersm@redhat.com>
Reviewed-by: Willian Rampazzo <willianr@redhat.com>
Message-Id: <20210430133414.39905-8-wainersm@redhat.com>
Signed-off-by: Cleber Rosa <crosa@redhat.com>