test: Generate one block for each send in wallet_import_rescan
test: Generate one block for each send in wallet_import_rescan

This ...
* ensures that enough coins are available/spendable, even when more
  variants are added
* ensures that all mempool txs are mined, even when more variants are
  added
* makes the test more specific to test that the confirmation height
  is properly reported and timestamps are correctly handled in the test
  logic
* prepares the test for a future, where blocks are skipped for rescan if
  they are deemed irrelevant by a filter (c.f. BIP157)

peercoin/peercoin,DigitalPandacoin/pandacoin,DigitalPandacoin/pandacoin,peercoin/peercoin,peercoin/peercoin,DigitalPandacoin/pandacoin,DigitalPandacoin/pandacoin,DigitalPandacoin/pandacoin,DigitalPandacoin/pandacoin,peercoin/peercoin,peercoin/peercoin,peercoin/peercoin