Refactoring shard engine

:Release Notes:

:Detailed Notes:
Refactoring MojDbShardEngine::Watcher

:Testing Performed:
Compiled and tested locally

:QA Notes:

:Issues Addressed:

Open-webOS-DCO-1.0-Signed-off-by: Maksym Sditanov <maxim.sditanov@lge.com>

Change-Id: I145fe0c52b347755be15fe7537639513d259b95c
Reviewed-on: https://g2g.palm.com/3915
Reviewed-by: Build Verification
Reviewed-by: Maksym Sditanov <maxim.sditanov@lge.com>
Tested-by: Maksym Sditanov <maxim.sditanov@lge.com>
Reviewed-by: Igor Kuksyuk <ikuksyuk@luxoft.com>