[PAN-1746] add 100-continue to RPC (#1727)

Retesteth waits a second for a 100 Continue when setting chain params. This
significantly slows down the test run.  Vertx can do it for us automatically.
Signed-off-by: Adrian Sutton <adrian.sutton@consensys.net>

ethereum/jsonrpc/src/main/java/tech/pegasys/pantheon/ethereum/jsonrpc/JsonRpcHttpService.java

@@ -166,7 +166,10 @@ public class JsonRpcHttpService {
     // Create the HTTP server and a router object.
     httpServer =
         vertx.createHttpServer(
-            new HttpServerOptions().setHost(config.getHost()).setPort(config.getPort()));
+            new HttpServerOptions()
+                .setHost(config.getHost())
+                .setPort(config.getPort())
+                .setHandle100ContinueAutomatically(true));
 
     // Handle json rpc requests
     final Router router = Router.router(vertx);