Use a fixed, 240s deadline for the daemons to reach agreement and poll
with a suitable frequency (.25s), rather than polling up to 100 times at
roughly 10s intervals.
Reduce the likelihood of false positive failures in the p2p
transaction propagation functional test by waiting up to a
maximum timeout for a transaction to propagate, rather than using a
fixed timeout, to reflect the random delay of Dandelion++ transaction
propagation. This strategy also speeds test execution in cases where
propagation occurs faster than the previously expected fixed delay.
