test: Test that an unconfirmed not-in-mempool chain is rebroadcast

The test checks that parent txs are broadcast before child txs.

The previous behavior is that the rebroadcasting would simply iterate mapWallet. As
mapWallet is a std::unsorted_map, the child can sometimes come before the parent and thus
be rebroadcast in the wrong order and fail the test.

test/functional/test_framework/messages.py

@@ -71,6 +71,7 @@ DEFAULT_DESCENDANT_LIMIT = 25  # default max number of in-mempool descendants
 # Default setting for -datacarriersize. 80 bytes of data, +1 for OP_RETURN, +2 for the pushdata opcodes.
 MAX_OP_RETURN_RELAY = 83
 
+DEFAULT_MEMPOOL_EXPIRY_HOURS = 336  # hours
 
 def sha256(s):
     return hashlib.sha256(s).digest()