Fix crash when shard engine not ready

:Release Notes:
When some service notify about media and mediadb have a lot of data, sometimes
possible crash of mojodb. Improve initalization of shard engine and
avoid crash of db8.

:Detailed Notes:
Remove pointer to MojDb from ShardEngine, make reference to MojDb and
init from default constructor
Remove from MojDbShardEngine ShardInfo struct, reduce file dependencies.
Remove std::auto from MojDbShardEngine to MojDbMediaLinkManager
Reduce file depenedencies to speed up compilation process

:Testing Performed:
Compiled and tested on device

:QA Notes:

:Issues Addressed:
[GF-57073] Excessive mojodb-luna crashes at location
           /usr/lib/libmojodb.so.3(_ZN5MojDb11requireOpenEv+0)

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

Change-Id: I65fd910af9ee33b429cb474f8113f3f7b9fb0836
Reviewed-on: https://g2g.palm.com/4326
Reviewed-by: Maksym Sditanov <maxim.sditanov@lge.com>
Reviewed-by: DCO Verification
Tested-by: Maksym Sditanov <maxim.sditanov@lge.com>
Reviewed-by: Oleksii Uratkin <oleksii.uratkin@lge.com>