Fix incorrect .name attribute for python program

It is always set to python3 even if we asked for python2...

(cherry picked from commit 445f08869b)

mesonbuild/modules/python.py

@@ -284,7 +284,7 @@ class PythonExternalProgram(ExternalProgram):
         if ext_prog is None:
             super().__init__(name, command=command, silent=True)
         else:
-            self.name = ext_prog.name
+            self.name = name
             self.command = ext_prog.command
             self.path = ext_prog.path
         self.info: T.Dict[str, str] = {}
@@ -515,13 +515,15 @@ class PythonModule(ExtensionModule):
         want_modules = mesonlib.extract_as_list(kwargs, 'modules')  # type: T.List[str]
         found_modules = []    # type: T.List[str]
         missing_modules = []  # type: T.List[str]
+        fallback = args[0] if args else ''
+        display_name = fallback or 'python'
 
         if len(args) > 1:
             raise InvalidArguments('find_installation takes zero or one positional argument.')
 
         name_or_path = state.environment.lookup_binary_entry(MachineChoice.HOST, 'python')
         if name_or_path is None and args:
-            name_or_path = args[0]
+            name_or_path = fallback
             if not isinstance(name_or_path, str):
                 raise InvalidArguments('find_installation argument must be a string.')
 
@@ -532,8 +534,8 @@ class PythonModule(ExtensionModule):
         if not name_or_path:
             python = PythonExternalProgram('python3', mesonlib.python_command)
         else:
-            tmp_python = ExternalProgram.from_entry('python3', name_or_path)
-            python = PythonExternalProgram('python3', ext_prog=tmp_python)
+            tmp_python = ExternalProgram.from_entry(display_name, name_or_path)
+            python = PythonExternalProgram(display_name, ext_prog=tmp_python)
 
             if not python.found() and mesonlib.is_windows():
                 pythonpath = self._get_win_pythonpath(name_or_path)