Consolidate boolean/mk_boolean conversion functions into a single location

Consolidate the module_utils, constants, and config functions that
convert values into booleans into a single function in module_utils.

Port code to use the module_utils.validate.convert_bool.boolean function
isntead of mk_boolean.

test/units/module_utils/parsing/test_convert_bool.py

@@ -0,0 +1,60 @@
+# -*- coding: utf-8 -*-
+# Copyright: (c) 2017 Ansible Project
+# License: GNU General Public License v3 or later (see COPYING or https://www.gnu.org/licenses/gpl-3.0.txt )
+
+# Make coding more python3-ish
+from __future__ import (absolute_import, division)
+__metaclass__ = type
+
+import pytest
+
+from ansible.module_utils.parsing.convert_bool import boolean
+
+
+class TestBoolean:
+    def test_bools(self):
+        assert boolean(True) is True
+        assert boolean(False) is False
+
+    def test_none(self):
+        with pytest.raises(TypeError):
+            assert boolean(None, strict=True) is False
+        assert boolean(None, strict=False) is False
+
+    def test_numbers(self):
+        assert boolean(1) is True
+        assert boolean(0) is False
+        assert boolean(0.0) is False
+
+# Current boolean() doesn't consider these to be true values
+#    def test_other_numbers(self):
+#        assert boolean(2) is True
+#        assert boolean(-1) is True
+#        assert boolean(0.1) is True
+
+    def test_strings(self):
+        assert boolean("true") is True
+        assert boolean("TRUE") is True
+        assert boolean("t") is True
+        assert boolean("yes") is True
+        assert boolean("y") is True
+        assert boolean("on") is True
+
+    def test_junk_values_nonstrict(self):
+        assert boolean("flibbity", strict=False) is False
+        assert boolean(42, strict=False) is False
+        assert boolean(42.0, strict=False) is False
+        assert boolean(object(), strict=False) is False
+
+    def test_junk_values_strict(self):
+        with pytest.raises(TypeError):
+            assert boolean("flibbity", strict=True)is False
+
+        with pytest.raises(TypeError):
+            assert boolean(42, strict=True)is False
+
+        with pytest.raises(TypeError):
+            assert boolean(42.0, strict=True)is False
+
+        with pytest.raises(TypeError):
+            assert boolean(object(), strict=True)is False