Add tests filters (#43221)

This will allow tests to be carried out condtionally if necessary
using regexp include and/or exclude filters
Reorganize imports into alphabetical order for easier insertion

test/units/modules/system/interfaces_file/test_interfaces_file.py

@@ -17,14 +17,15 @@
 
 from units.compat import unittest
 from ansible.modules.system import interfaces_file
-import os
-import json
-import io
-import inspect
 from shutil import copyfile, move
 import difflib
-import tempfile
+import inspect
+import io
+import json
+import os
+import re
 import shutil
+import tempfile
 
 
 class AnsibleFailJson(Exception):
@@ -50,8 +51,13 @@ golden_output_path = os.path.join(os.path.dirname(__file__), 'fixtures', 'golden
 
 
 class TestInterfacesFileModule(unittest.TestCase):
-    def getTestFiles(self):
-        return next(os.walk(fixture_path))[2]
+    def getTestFiles(self, include_filter=None, exclude_filter=None):
+        flist = next(os.walk(fixture_path))[2]
+        if include_filter:
+            flist = filter(lambda x: re.match(include_filter, x), flist)
+        if exclude_filter:
+            flist = filter(lambda x: not re.match(exclude_filter, x), flist)
+        return flist
 
     def compareFileToBackup(self, path, backup):
         with open(path) as f1: