qemu/tests/cpuid: fix escaping of "-cpu ?" command

The command being run is a shell command, so running it as "-cpu ?"
without any quotes around "?" will make the shell expand "?" to the list
of filenames with one letter in the current directory.
Let's fix this by properly escaping the question mark.
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>

qemu/tests/cpuid.py

@@ -72,7 +72,7 @@ def run_cpuid(test, params, env):
         """
         Get all cpu models from qemu -cpu help text.
 
-        @param qemu_cpu_help_text: text produced by <qemu> -cpu ?
+        @param qemu_cpu_help_text: text produced by <qemu> -cpu '?'
         @return: list of cpu models
         """
 
@@ -81,7 +81,7 @@ def run_cpuid(test, params, env):
 
     class test_qemu_cpu_models_list(MiniSubtest):
         """
-        check CPU models returned by <qemu> -cpu ? are what is expected
+        check CPU models returned by <qemu> -cpu '?' are what is expected
         """
         def test(self):
             """
@@ -91,7 +91,7 @@ def run_cpuid(test, params, env):
                 raise error.TestNAError("define cpu_models parameter to check "
                                         "supported CPU models list")
 
-            cmd = qemu_binary + " -cpu ?"
+            cmd = qemu_binary + " -cpu '?'"
             result = utils.run(cmd)
             qemu_models = extract_qemu_cpu_models(result.stdout)
             cpu_models = params.get("cpu_models").split()
@@ -177,7 +177,7 @@ def run_cpuid(test, params, env):
         """
         def test(self):
             if params.get("cpu_models") is None:
-                cmd = qemu_binary + " -cpu ?"
+                cmd = qemu_binary + " -cpu '?'"
                 result = utils.run(cmd)
                 cpu_models = set(extract_qemu_cpu_models(result.stdout))
             else: