Update prune test to account for larger minimum pruning size.
Update prune test to account for larger minimum pruning size.

Create 2MB blocks instead of 1MB blocks.

dagurval/bitcoinxt,bitcoinxt/bitcoinxt,bitcoinxt/bitcoinxt,bitcoinxt/bitcoinxt,bitcoinxt/bitcoinxt,dagurval/bitcoinxt,dagurval/bitcoinxt,dagurval/bitcoinxt,dagurval/bitcoinxt,bitcoinxt/bitcoinxt,dagurval/bitcoinxt,bitcoinxt/bitcoinxt