replace imp module with importlib

When trying to run cloudbase-init using Python 3.12, it errors out
ModuleNotFoundError: No module named 'imp'.

The 'imp' module was replaced with similar functionality from module
importlib.

These two implementations are equivalent:

```python
import imp

import os
import site

wmi_path = None
for packages_path in site.getsitepackages():
    path = os.path.join(packages_path, "wmi.py")
    if os.path.isfile(path):
        wmi_path = path
        break

wmi_module_name = "wmi"
wmi_module = imp.load_source(wmi_module_name, wmi_path)

```

```python
import importlib.util

import os
import site

wmi_path = None
for packages_path in site.getsitepackages():
    path = os.path.join(packages_path, "wmi.py")
    if os.path.isfile(path):
        wmi_path = path
        break

wmi_module_name = "wmi"
wmi_module_spec = importlib.util.spec_from_file_location(wmi_module_name, wmi_path)
wmi_module = importlib.util.module_from_spec(wmi_module_spec)
wmi_module_spec.loader.exec_module(wmi_module)
```

Fixes: #139

Change-Id: I6490c6d9922efea26ab8d167a0d6e41ce34d6c2c
Signed-off-by: Adrian Vladu <avladu@cloudbasesolutions.com>

cloudbaseinit/tests/utils/test_classloader.py

@@ -35,12 +35,11 @@ class ClassLoaderTest(unittest.TestCase):
     def setUp(self):
         self._loader = classloader.ClassLoader()
 
-    @mock.patch('imp.load_compiled')
-    @mock.patch('imp.load_source')
-    def test_load_module_py(self, mock_source, mock_compiled):
+    @mock.patch('cloudbaseinit.utils.classloader.load_module_from_path')
+    def test_load_module_py(self, mock_source_compiled):
         mock_py = os.path.join(_create_tempfile(), "mock.py")
         mock_pyc = os.path.join(_create_tempfile(), "mock.pyc")
-        mock_source.return_value = mock_compiled.return_value = None
+        mock_source_compiled.return_value = None
         result_module_py = self._loader.load_module(mock_py)
         result_module_pyc = self._loader.load_module(mock_pyc)
         self.assertIsNone(result_module_py)

cloudbaseinit/tests/utils/windows/test_wmi_loader.py

@@ -32,23 +32,24 @@ def test_load_pymi(self):
             wmi_loader = importlib.import_module(MODPATH)
             self.assertEqual(mock.sentinel.wmi, wmi_loader.wmi())
 
-    @mock.patch('imp.load_source')
+    @mock.patch('cloudbaseinit.utils.classloader.load_module_from_path')
     @mock.patch('os.path.isfile')
-    def test_load_legacy_wmi(self, mock_isfile, mock_load_source):
+    def test_load_legacy_wmi(self, mock_isfile, mock_load_module_from_path):
         mock_isfile.return_value = True
 
         mock_site = mock.MagicMock()
         fake_site_path = "fake_site_path"
         mock_site.getsitepackages.return_value = [fake_site_path]
-        mock_load_source.return_value = mock.sentinel.wmi
+        mock_load_module_from_path.return_value = mock.sentinel.wmi
 
         with mock.patch.dict('sys.modules', {'wmi': None, 'site': mock_site}):
             wmi_loader = importlib.import_module(MODPATH)
             self.assertEqual(mock.sentinel.wmi, wmi_loader.wmi())
 
         fake_wmi_path = os.path.join(fake_site_path, "wmi.py")
         mock_isfile.assert_called_once_with(fake_wmi_path)
-        mock_load_source.assert_called_once_with("wmi", fake_wmi_path)
+        mock_load_module_from_path.assert_called_once_with(
+            "wmi", fake_wmi_path)
 
     @mock.patch('os.path.isfile')
     def test_load_legacy_wmi_fail(self, mock_isfile):

cloudbaseinit/utils/classloader.py

@@ -12,7 +12,7 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-import imp
+import importlib
 import os
 
 from oslo_log import log as oslo_logging
@@ -21,6 +21,14 @@
 LOG = oslo_logging.getLogger(__name__)
 
 
+def load_module_from_path(module_name, path):
+    spec = importlib.util.spec_from_file_location(module_name, path)
+    module = importlib.util.module_from_spec(spec)
+    spec.loader.exec_module(module)
+
+    return module
+
+
 class ClassLoader(object):
 
     def load_class(self, class_path):
@@ -32,9 +40,7 @@ def load_class(self, class_path):
     def load_module(self, path):
         module_name, file_ext = os.path.splitext(os.path.split(path)[-1])
 
-        if file_ext.lower() == '.py':
-            module = imp.load_source(module_name, path)
-        elif file_ext.lower() == '.pyc':
-            module = imp.load_compiled(module_name, path)
+        if file_ext.lower() in ['.py', '.pyc']:
+            module = load_module_from_path(module_name, path)
 
         return module

cloudbaseinit/utils/windows/wmi_loader.py

@@ -12,13 +12,13 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-import imp
 import os
 import site
 
 from oslo_log import log as oslo_logging
 
 from cloudbaseinit import exception
+from cloudbaseinit.utils.classloader import load_module_from_path
 
 LOG = oslo_logging.getLogger(__name__)
 
@@ -41,4 +41,4 @@ def wmi():
         if wmi_path is None:
             raise exception.ItemNotFoundException("wmi module not found")
 
-        return imp.load_source("wmi", wmi_path)
+        return load_module_from_path("wmi", wmi_path)