IMPALA-13826: Migrate from imp to importlib in the config generator

Python has deprecated the 'imp' package in Python 3.4, and removed it in
Python 3.12. The deprecation has also started throwing warnings in
versions before 3.12.

The template generator used a single call to imp.load_source to load the
template Python file. This is now replaced with code snippet published
in Python's official documentation.

Change-Id: I472d093eeaac97a380d444a1756b54f825b2d031
Reviewed-on: http://gerrit.cloudera.org:8080/22582
Reviewed-by: Zoltan Borok-Nagy <boroknagyz@cloudera.com>
Tested-by: Laszlo Gaal <laszlo.gaal@cloudera.com>

bin/generate_xml_config.py

@@ -40,7 +40,6 @@ REPL:
 """
 
 from __future__ import absolute_import, division, print_function
-import imp
 import os
 import re
 import sys
@@ -95,6 +94,33 @@ def dump_config(d, source_path, out):
   print("</configuration>", file=out)
 
 
+def load_source_with_importlib(modname, filename):
+  """"Emulate imp.load_source() of Python2 for Python3 using importlib
+      Code taken from published Python documentation, see
+      https://docs.python.org/3/whatsnew/3.12.html#imp"""
+  import importlib.util
+  import importlib.machinery
+
+  loader = importlib.machinery.SourceFileLoader(modname, filename)
+  spec = importlib.util.spec_from_file_location(modname, filename, loader=loader)
+  module = importlib.util.module_from_spec(spec)
+  # The module is always executed and not cached in sys.modules.
+  # Uncomment the following line to cache the module.
+  # sys.modules[module.__name__] = module
+  loader.exec_module(module)
+  return module
+
+
+def import_template(name, module_path):
+  """Handle module import differences between Python2 and Python3"""
+  mod = None
+  if sys.version_info.major < 3:
+    import imp
+    mod = imp.load_source('template', module_path)
+  else:
+    mod = load_source_with_importlib(name, module_path)
+  return mod
+
 def main():
   if len(sys.argv) != 3:
     print("usage: {prog} <template> <out>".format(prog=sys.argv[0]), file=sys.stderr)
@@ -102,7 +128,7 @@ def main():
 
   _, in_path, out_path = sys.argv
   try:
-    mod = imp.load_source('template', in_path)
+    mod = import_template('template', in_path)
   except:  # noqa
     print("Unable to load template: %s" % in_path, file=sys.stderr)
     raise