Set correct service dialog checkbox field values and validate properly if Required is set

* The fix on 5.4/5.3 will force all values coming in from the UI to be "t" or "f", just like the default value is set to.

* The fix on 5.2 will allow the invalid values sent in from the UI of "1" for true and "null" for false to be handled by the back end (as well as "t" and "f") so existing automate custom code doesn't break.

https://bugzilla.redhat.com/show_bug.cgi?id=1132014