Provide Dilated Timeouts for Java Testkit

[jlprat]

As discovered in #1238, Java Testkit can't benefit of the dilated tests.
The current timeout when using Scala Testkit is 1 second (dilated) while the Java one is just 3 seconds.

In order to let Java Testkit use dilated, the RouteTest should extend JavaTestKit (that is where the dilated method is defined).

[jiminhsieh]

I found JavaTestKit prepare to deprecate since Akka 2.5.0. It would be replace by akka.testkit.javadsl.TestKit. Do we still need to fix this? I also found akka.http.javadsl.testkit.RouteTest could not just simply extend JavaTestKit. It already extended abstract class - akka.http.javadsl.server.AllDirectives. Maybe I just misunderstand what your idea. Thanks!

[jlprat]

That might well be (deprecation)! I guess I was checking the 2.4.x series (which Akka HTTP depends on).
Basically, what I meant is that https://github.com/akka/akka-http/blob/master/akka-http-testkit/src/main/scala/akka/http/javadsl/testkit/RouteTest.scala#L36 this should have a dilated timeout.

[raboof]

(just to clarify, in case someone stumbles upon this ticket: while Akka HTTP indeed depends on Akka 2.4.x, it also works with Akka 2.5.x as those are binary compatible. We plan to update the dependency as part of #1151)

[jrudolph]

Fixed in #1272.