fullblocktests: Improve vote on wrong block tests.
fullblocktests: Improve vote on wrong block tests.

This improves the test which checks for votes on the wrong block by
creating a new commitment script and testing 3 different scenarios:

- Ticket that commits to the parent of the correct block to ensure that
  the code under test is not just failing due to a hash that doesn't
  exist
- Ticket that commits to the correct block hash and wrong block height
- Ticket the commits to the correct block height and wrong block hash

jrick/dcrd,decred/dcrd,jrick/dcrd,decred/dcrd