Consider retry logic when submitting roots to Hoku

[stbrody]

What if the gas is too low? What if waiting for the txn to mine times out? What if Hoku is unavailable?

For many of these the answer might be to just throw out the batch and try everything again from the beginning, but we should think about if that is actually good enough in all cases, especially in the cases of the gas is too low. If the txn fails to be included in a block at all because the gas we are sending is too low, we might need to increase how much gas we are sending in order to get the txn ever included in a block. If we time out waiting for the txn to be included in a block, it still could be included after we give up, which could cause our nonce to get of sync in the SDK.