Improve blocksdir functional test.
Improve blocksdir functional test.

A new node should not create an unused `blocks` directory in the root of
the data directory when `-testnet` or `-regtest` is specified.

chaincoin/chaincoin,chaincoin/chaincoin,chaincoin/chaincoin,chaincoin/chaincoin,chaincoin/chaincoin,chaincoin/chaincoin