scripts/qmp-shell: Fix "FuzzyJSON" parser

I'm not sure when this regressed (Or maybe if it was ever working right
to begin with?), but the Python AST requires you to change "Names" to
"Constants" in order to truly convert `false` to `False`.

Signed-off-by: John Snow <jsnow@redhat.com>
Message-id: 20210607200649.1840382-24-jsnow@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>

scripts/qmp/qmp-shell

@@ -95,18 +95,19 @@ class QMPShellError(Exception):
 class FuzzyJSON(ast.NodeTransformer):
     """
     This extension of ast.NodeTransformer filters literal "true/false/null"
-    values in an AST and replaces them by proper "True/False/None" values that
-    Python can properly evaluate.
+    values in a Python AST and replaces them by proper "True/False/None" values
+    that Python can properly evaluate.
     """
 
     @classmethod
-    def visit_Name(cls, node):  # pylint: disable=invalid-name
+    def visit_Name(cls,  # pylint: disable=invalid-name
+                   node: ast.Name) -> ast.AST:
         if node.id == 'true':
-            node.id = 'True'
+            return ast.Constant(value=True)
         if node.id == 'false':
-            node.id = 'False'
+            return ast.Constant(value=False)
         if node.id == 'null':
-            node.id = 'None'
+            return ast.Constant(value=None)
         return node
 
 
@@ -174,10 +175,9 @@ class QMPShell(qmp.QEMUMonitorProtocol):
             # Try once again as FuzzyJSON:
             try:
                 tree = ast.parse(val, mode='eval')
-                return ast.literal_eval(FuzzyJSON().visit(tree))
-            except SyntaxError:
-                pass
-            except ValueError:
+                transformed = FuzzyJSON().visit(tree)
+                return ast.literal_eval(transformed)
+            except (SyntaxError, ValueError):
                 pass
         return val