WL#2494: Handle diverse partition sets for scans in NDB API

As part of WL 1354 it will be possible to discover more detailed information
about which partitions that are necessary to scan for certain queries.

This discovery could lead to the following cases.

1) Only one partition needs to be scanned
2) All partitions need to be scanned
3) Start partition and End Partition for RANGE partitions
4) Bitvector of Partitions to use for LIST partitions

1) and 2) is already supported.

There will be functions that deliver results on which partitions to use for
3) and 4)

There needs to be support for this in the NDB API for all types of scans
For this work there needs to be work done in the NDB API and in DBTC to support
scanning a subset of the fragments.