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.

lib/ansible/module_utils/parsing/convert_bool.py

@@ -0,0 +1,26 @@
+# Copyright: 2017, Ansible Project
+# License: GNU General Public License v3 or later (see COPYING or https://www.gnu.org/licenses/gpl-3.0.txt )
+
+from ansible.module_utils.six import binary_type, text_type
+from ansible.module_utils._text import to_text
+
+
+BOOLEANS_TRUE = frozenset(('y', 'yes', 'on', '1', 'true', 't', 1, 1.0, True))
+BOOLEANS_FALSE = frozenset(('n', 'no', 'off', '0', 'false', 'f', 0, 0.0, False))
+BOOLEANS = BOOLEANS_TRUE.union(BOOLEANS_FALSE)
+
+
+def boolean(value, strict=True):
+    if isinstance(value, bool):
+        return value
+
+    normalized_value = value
+    if isinstance(value, (text_type, binary_type)):
+        normalized_value = to_text(value, errors='surrogate_or_strict').lower()
+
+    if normalized_value in BOOLEANS_TRUE:
+        return True
+    elif normalized_value in BOOLEANS_FALSE or not strict:
+        return False
+
+    raise TypeError('%s is not a valid boolean.  Valid booleans include: %s' % (to_text(value), ', '.join(repr(i) for i in BOOLEANS)))