Resubmission failed message changed from error to warning

It is possible the resubmission failed because the transaction has just
been mined. It's not worth logging it as an ERROR especially that the first
transaction was submitted (and that's always the case before we get to
mining monitoring).

Author: pdyraga

pkg/chain/ethereum/ethutil/mine_waiter.go

@@ -127,7 +127,7 @@ func (mw MiningWaiter) ForceMining(
 		)
 		transaction, err = resubmitFn(gasPrice)
 		if err != nil {
-			logger.Errorf("failed resubmitting TX with a higher gas price: [%v]", err)
+			logger.Warningf("could not resubmit TX with a higher gas price: [%v]", err)
 			return
 		}
 	}