Improve searching when external devices change status

:Release Notes:
Performance and stability improvment for shard logic in MojDbShardEngine

:Detailed Notes:
- Add MojDbShardEngine::getByDeviceUuid
- Fix and improve searching in MojDbShardEngine::Watcher::handleShardInfoSlot

:Testing Performed:
./gtest_db_core -send -n 1 -f luna://com.palm.db/listActiveMedia '{}'
luna-send -n 1 -f luna://com.palm.db/listActiveMedia '{}'

:QA Notes:
luna-send -n 1 -f luna://com.palm.db/listActiveMedia '{}' now return list of active devices

: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: I3c480ab5326a3641fa3204142adf3ebe3f717347
Reviewed-on: https://g2g.palm.com/3236
Reviewed-by: Build Verification
Reviewed-by: Roger Stringer <roger.stringer@lge.com>
Tested-by: Roger Stringer <roger.stringer@lge.com>