Stop using deprecated functions in std Python lib

This PR stops using the following deprecated functions in std Python lib.

* parser.readfp
  We should use parser.read_file(readline_generator(fp))[1].
* importing modules from collections directly.
  We should use collections.abc instead of using collections directly.[2]

--
[1]: https://docs.python.org/3/library/configparser.html#configparser.ConfigParser.readfp
[2]: https://github.com/python/cpython/pull/5460

Task: 44767
Story: 2009917
Change-Id: I61bf4299ad2acd8ee26b4aab66875b10287020e1

trove/common/stream_codecs.py

@@ -207,7 +207,7 @@ class IniCodec(StreamCodec):
 
     def deserialize(self, stream):
         parser = self._init_config_parser()
-        parser.readfp(self._pre_parse(stream))
+        parser.read_file(self._pre_parse(stream))
 
         return {s: {k:
                     StringConverter({None: self._default_value}).to_objects(v)

trove/tests/config.py

@@ -21,7 +21,7 @@ environments if we choose to.
 
 """
 
-from collections import Mapping
+from collections.abc import Mapping
 from datetime import datetime
 import json
 import os