Correct TendermintMachine sleep on construction

For logging purposes, I added code to handle negative time till start. I forgot
to only sleep on positive time till start.

Should fix the recent CI failure.

coordinator/tributary/tendermint/src/lib.rs

@@ -281,7 +281,9 @@ impl<N: Network + 'static> TendermintMachine<N> {
         );
 
         // If the last block hasn't ended yet, sleep until it has
-        sleep(time_until).await;
+        if !negative {
+          sleep(time_until).await;
+        }
 
         let signer = network.signer();
         let validators = network.signature_scheme();