Add base-64 ID value to listActiveMedia API return set

:Release Notes:
Performance and stability improvment for shard logic

:Detailed Notes:
MojDbServiceHandler::handleListActiveMedia return base64 shard id

:Testing Performed:
./gtest_db_core -send -n 1 -f luna://com.palm.db/listActiveMedia '{}'
luna-send -n 1 -f luna://com.palm.db/listActiveMedia '{}'
luna-send -n 1 -f luna://com.palm.db/shardInfo '{"shardId":"+HoRYV"}'

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

: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: Ic845929cd1b7912106cae52a4b89ee1e07c4ac99
Reviewed-on: https://g2g.palm.com/3237
Reviewed-by: Build Verification
Reviewed-by: Roger Stringer <roger.stringer@lge.com>
Tested-by: Roger Stringer <roger.stringer@lge.com>