[SPARKL-37]

- Corrected bug: When a user executes a kettle endpoint she may receive the cached result value of another user.
- Corrected bug: When a user specifies in the ktr/kjb cpk.cache.timeToLiveSeconds=0, no result is cached as opposed to set time to live to infinity.
- The value of  CPK parameters that are not declared in the ktr / kjb file are no longer injected. Only values of declared CPK parameters are injected.
- Refactored KettleElementHelper class and auxiliary functions/structures related to kettle parameter handling in general.