OPENDJ-960 (CR-1844) HTTP Connection Handler - Validate http-config.json file 

Enhanced JsonValue by adding a record/verify mode for key accesses.
Client code must call recordKeyAccesses() to verifyAllKeysAccessed().
When yhere is an an unaccessed key, a JsonException will be thrown and all unaccessed keys will be reported (unaccessed keys located under other unaccessed keys are not reported to reduce noise).


HTTPConnectionHandler.java:
In createAndRegisterServlet(), enabled the record mode before accessing the keys, then verify all the keys have been accessed after we are done with the JSON config.

JsonValue.java:
Added recordKeyAccesses() and verifyAllKeysAccessed().

JsonValueKeyAccessChecker.java, JsonValueKeyAccessCheckerTest.java: ADDED