Use importlib instead of imp for Python >= 3.5

The imp module is deprecated and disappears in Python 3.12.
In slapos.recipe.cmmi, importlib/imp is used to run scripts
loaded directly from files. The importlib version is the now
recommanded way for Python 3.5+.

slapos/recipe/cmmi/__init__.py

 import errno
-import imp
 import logging
 import os
 import re
@@ -17,6 +16,20 @@ from ..utils import (
 # from slapos.recipe.build
 from .. import downloadunpacked
 
+if sys.version_info >= (3, 5):
+    # See https://docs.python.org/3/library/importlib.html#importing-a-source-file-directly
+    import importlib.util
+    def module_from_file_location(name, path):
+        spec = importlib.util.spec_from_file_location(name, path)
+        module = importlib.util.module_from_spec(spec)
+        sys.modules[name] = module
+        spec.loader.exec_module(module)
+        return module
+else:
+    # BBB Python2, Python < 3.5
+    from imp import load_source as module_from_file_location
+
+
 startup_environ = os.environ.copy()
 
 # backport of shlex.quote from Python 3.3
@@ -132,7 +145,7 @@ class Recipe(EnvironMixin):
         try:
             if not is_temp:
                 filename = os.path.abspath(filename)
-            module = imp.load_source('script', filename)
+            module = module_from_file_location('script', filename)
             script = getattr(module, callable.strip())
             try:
                 script(self.options, self.buildout, self.environ)