message: Fix spurious failures in mempool_packages.py
  Add a syncronization point to wait for the transactions to be
  resurrencted in the mempool before proceeding.
diff: @@ -161,6 +161,8 @@ class MempoolPackagesTest(BitcoinTestFramework):
  self.nodes[1].invalidateblock(self.nodes[1].getbestblockhash())
  # Now check that the transaction is in the mempool, with the right modified fee
  + waitFor(30, lambda: self.nodes[1].getmempoolinfo()['size'] == 5)
  + waitFor(30, lambda: self.nodes[0].getmempoolinfo()['size'] == 25)
  mempool = self.nodes[0].getrawmempool(True)
  descendant_fees = 0
  