Add toggle to control invalid character substitution in group names (#52748)

* make add_group return proper name
* ensure central transform/check
* added 'silent' option to avoid spamming current users
  those already using the plugins were used to the transformations, so no need to alert them
* centralized valid var names
* dont display dupes
* comment on regex
* added regex tests
  ini and script will now warn about deprecation
* more complete errormsg

test/units/regex/test_invalid_var_names.py

@@ -0,0 +1,27 @@
+# Make coding more python3-ish
+from __future__ import (absolute_import, division, print_function)
+__metaclass__ = type
+
+from units.compat import unittest
+
+from ansible import constants as C
+
+
+test_cases = (('not-valid', ['-'], 'not_valid'), ('not!valid@either', ['!', '@'], 'not_valid_either'), ('1_nor_This', ['1'], '__nor_This'))
+
+
+class TestInvalidVars(unittest.TestCase):
+
+    def test_positive_matches(self):
+
+        for name, invalid, sanitized in test_cases:
+            self.assertEqual(C.INVALID_VARIABLE_NAMES.findall(name), invalid)
+
+    def test_negative_matches(self):
+        for name in ('this_is_valid', 'Also_1_valid', 'noproblem'):
+            self.assertEqual(C.INVALID_VARIABLE_NAMES.findall(name), [])
+
+    def test_get_setting(self):
+
+        for name, invalid, sanitized in test_cases:
+            self.assertEqual(C.INVALID_VARIABLE_NAMES.sub('_', name), sanitized)