Improved code for moving migrated files in the store directory

@tinwelint I did and several tests failed. I believe we have to copy them since we have to deduplicate properties when migrating from 1.9 to 2.0. See https://github.com/neo4j/neo4j/blob/master/community/kernel/src/main/java/org/neo4j/kernel/impl/storemigration/StoreMigrator.java#L192 and https://github.com/neo4j/neo4j/blob/master/community/neo4j/src/test/java/upgrade/StoreMigratorIT.java#L115