Refactor ncmp request handlers (fix async issue)

Refactor ncmp request handlers (fix async issue)

- simplified request handlers (sub)classes (no more need for default interface)
- fix issue with async execution of data operation requests (wasn't really async)
- removed redundant (unreachable) check in production code
- Improved code coverage (branches) ncmp request handlers added UNIT test
- removed MVC test scenarios now covered by appropriate unit level tests
- applied Spock Polling Condition for verifying async call

Issue-ID: CPS-475
Signed-off-by: ToineSiebelink <toine.siebelink@est.tech>
Change-Id: Ibe601c709de65080fa8898f2419fdbd92c5ba27d