This is a subset of the more controversial https://github.com/bitcoin/bitcoin/pull/12407, but this also adds a test demonstrating the bug.

In InvalidateBlock, we're calling NotifyBlockTip with the now-invalid block's prev regardless of what chain the ancestor block is on. This could create numerous issues, but it at least screws up `waitforblockheight` (or anything else relying on `rpc/blockchain.cpp:latestblock`) when InvalidateBlock is called on a block not in chainActive, which can happen via RPC.

Only call NotifyBlockTip when the block being marked invalid is on the active chain.

make check
test_runner.py