MB-12573 Adapt forestdb_dump tool to be compatible with multi KVS mode

- All KV store info are printed in the DB header section.

- Added one more option: --kvs [KV store name]. If this option is passed,
only documents belonging to the specified KV store are displayed.

Change-Id: I64dac7022d1fe8abda2f2c826491cf7e3fe3dcf1