Boolean options: use strict checking

Boolean options (such as "--protected" for glance md-namespace-update)
should accept a limited amount of valid values, rather than assuming an
"invalid" value means "False".

The following values (no matter the case) will now be interpreted as
True: ‘t’,’true’, ‘on’, ‘y’, ‘yes’, or ‘1’.

The following values (no matter the case) will now be interpreted as
False: ‘f’, ‘false’, ‘off’, ‘n’, ‘no’, or ‘0’.

Change-Id: I0e7942045d883ac398bab4a7a85f2b4ac9b1ed8c
Closes-Bug: #1607317

releasenotes/notes/boolean-properties-strict-checking-bdd624b5da81e723.yaml

@@ -0,0 +1,12 @@
+---
+prelude: >
+fixes:
+  - |
+    * Bug 1607317_: metadata def namespace update CLI is not working as expected for parameter "protected"
+
+    .. _1607317: https://code.launchpad.net/bugs/1607317
+other:
+  - |
+    Boolean arguments now expect one of the following values: '0', '1', 'f',
+    'false', 'n', 'no', 'off', 'on', 't', 'true', 'y', 'yes'
+    (case-insensitive). This will not change anything for most users.