abc_mining_basic runs the same tests on two different nodes.
Since the tests expect to activate Axion, a race condition exists where
node1 may sync some of node0's blocks before the tests complete for node1,
resulting in an unexpected Axion activation.
Normally, we could override setup_network() to ensure the nodes do not talk
to each other. However, since getblocktemplate expects a peer, it's easier to
leave them connected and simply invalidate any blocks mined by the other node to
ensure a clean Axion activation.