Parent/child: Reduce memory usage in top children query.

Closes #8165
Closes #8160
Tests: Adding additional debug info to upgrade test.
Boostrap: Log startup exception to console if needed and to file as error

Closes #6581
Change IndexPrimaryShardNotAllocatedException from 409 (RestStatus.CONFLICT) to 500 (RestStatus.INTERNAL_SERVER_ERROR)

Closes #7632, Closes #7987