IndexUpdate should not reindex newly imported index definitions

IndexUpdate currently decides to reindex any index which is not found in before state i.e. state corresponding to the last checkpointed state. This was done to support cases like OAK-1874 where a new index may not have reindex flag set to true.

For importing new indexed definitions i.e. where indexing is already done out-of-band by oak-run this poses problem as this new index definition would not be present in before state.

To account for that this logic should be changed to check if the new index definition is already indexed or not. This can be checked by checking for presence of any hidden node under index definitions. If present then it means that index is already indexed so no need to reindex