Ensures legacy stores with Johnny Labels can be migrated

where Johnny is a node with an awful lot of labels, such that it spills
over into dynamic records.

Solved by creating the neostore upfront, for the batch importer to later
open. In between the node dynamic label store can be copied over.
Merge pull request #3339 from tinwelint/2.2-bip-store-migrator-dyn-labels

Ensures legacy stores with Johnny Labels can be migrated