Previously these functions would infinitely loop if sync failed;
now they have a default timeout of 60 seconds, after which an
AssertionError is raised.
sync_blocks() has also been improved and now compares the tip
hash of each node, rather than just using block count.
Zcash: Kept block count check for a couple of tests where we use it.
The p2p_nu_peer_management and rewind_index RPC tests still start from
Sprout, because they are explicitly (and only) testing network behaviour
across network upgrades.
The mempool_tx_input_limit test is removed because the flag has been
ignored since Sapling activation, and will be removed at some point in
the near future.
Suhas Daftuar
MarcoFalke
Kris Nuttycombe
mdr0id
Jack Grigg
Daira Hopwood