Replace oslo_utils.fnmatch with fnmatch

The oslo_utils.fnmatch module was added to solve an issue in py2.7 but
it is no longer required because py2.7 is no longer supported.
The module was deprecated since oslo.utils 4.9.1[1] and the stdlib's
fnmatch module should be used instead.

[1] 4c893c92f551c9dd2a7cfbe7ae8171ad8139df0b

Change-Id: If6ea16bbad5a7454e3a0f190c5a5e8da17f01a89

barbican/plugin/snakeoil_ca.py

@@ -15,6 +15,7 @@
 
 import base64
 import datetime
+import fnmatch
 import os
 import re
 import subprocess  # nosec
@@ -23,7 +24,6 @@ import uuid
 
 from OpenSSL import crypto
 from oslo_config import cfg
-from oslo_utils import fnmatch
 from oslo_utils import uuidutils
 
 from barbican.common import config