MojDbShardEngine: Refactoring and bug fixes

:Release Notes:
Performance and stability improvements for shard logic

:Detailed Notes:
- Remove unrequired functions from MojDbShardEngine
- Remove mp_db checking macros
- If shard not found, function MojDbShardEngine::update returns error
- Add returning of field "activity" from MojDbShardEngine::get
- MojDbShardEngine::get return whether object found or not
- Add MojDbShardEngine::convertId functions
- Add error checking inside MojDbServiceHandler class

:Testing Performed:
./gtest_db_core

:QA Notes:

:Issues Address:
[GF-33473] New 'listActiveMedia' never lists active media

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

Change-Id: I62575fcf94ca74dc2ed7d9907f0cbbd3c7ec3a08
Reviewed-on: https://g2g.palm.com/3235
Reviewed-by: Build Verification
Reviewed-by: Roger Stringer <roger.stringer@lge.com>
Tested-by: Roger Stringer <roger.stringer@lge.com>