Fix some imports for py310

Between this and the (unreleased) pyeclib fix, I see unit and func tests
passing on py310. Haven't tried probe tests, yet.

Change-Id: Iacf66eda75fed6bf96900107250f393227c57ae5

swift/common/middleware/s3api/s3response.py

@@ -14,7 +14,10 @@
 # limitations under the License.
 
 import re
-from collections import MutableMapping
+try:
+    from collections.abc import MutableMapping
+except ImportError:
+    from collections import MutableMapping  # py2
 from functools import partial
 
 from swift.common import header_key_dict

swift/common/swob.py

@@ -35,7 +35,11 @@ place to keep Swift working every time webob decides some interface
 needs to change.
 """
 
-from collections import defaultdict, MutableMapping
+from collections import defaultdict
+try:
+    from collections.abc import MutableMapping
+except ImportError:
+    from collections import MutableMapping  # py2
 import time
 from functools import partial
 from datetime import datetime

test/unit/__init__.py

@@ -22,7 +22,11 @@ import logging
 import logging.handlers
 import sys
 from contextlib import contextmanager, closing
-from collections import defaultdict, Iterable
+from collections import defaultdict
+try:
+    from collections.abc import Iterable
+except ImportError:
+    from collections import Iterable  # py2
 import itertools
 from numbers import Number
 from tempfile import NamedTemporaryFile