Preserve http2 option when doing from javadsl to scaladsl

The only information passed from javadsl to the scaladsl in Http
was the context which for Http connections was always the default one
meaning that setting http2 always had no effect.

akka-http-core/src/main/scala/akka/http/javadsl/ConnectHttp.scala

@@ -7,8 +7,9 @@ package akka.http.javadsl
 import java.util.Locale
 import java.util.Optional
 
-import akka.annotation.{ DoNotInherit, InternalApi }
+import akka.annotation.{DoNotInherit, InternalApi}
 import akka.http.javadsl.model.Uri
+import akka.http.scaladsl.HttpConnectionContext
 import akka.http.scaladsl.UseHttp2.Negotiated
 
 @DoNotInherit
@@ -23,7 +24,7 @@ abstract class ConnectHttp {
   final def effectiveHttpsConnectionContext(fallbackContext: HttpsConnectionContext): HttpsConnectionContext =
     connectionContext.orElse(fallbackContext)
 
-  final def effectiveConnectionContext(fallbackContext: ConnectionContext): ConnectionContext =
+  def effectiveConnectionContext(fallbackContext: ConnectionContext): ConnectionContext =
     if (connectionContext.isPresent) connectionContext.get()
     else fallbackContext
 
@@ -167,6 +168,9 @@ final class ConnectHttpImpl(val host: String, val port: Int, val http2: UseHttp2
   def isHttps: Boolean = false
 
   def connectionContext: Optional[HttpsConnectionContext] = Optional.empty()
+
+  override def effectiveConnectionContext(fallbackContext: ConnectionContext): ConnectionContext =
+    HttpConnectionContext(http2.asScala)
 }
 
 /** INTERNAL API */

akka-http-core/src/main/scala/akka/http/scaladsl/ConnectionContext.scala

@@ -9,7 +9,7 @@ import akka.stream.TLSProtocol._
 import com.typesafe.sslconfig.akka.AkkaSSLConfig
 
 import scala.collection.JavaConverters._
-import java.util.{ Optional, Collection ⇒ JCollection }
+import java.util.{Optional, Collection => JCollection}
 
 import akka.http.scaladsl.UseHttp2.Negotiated
 import javax.net.ssl._
@@ -98,6 +98,7 @@ final class HttpsConnectionContext(
 sealed class HttpConnectionContext(http2: UseHttp2) extends akka.http.javadsl.HttpConnectionContext(http2) with ConnectionContext {
   def this() = this(Negotiated)
 }
+
 final object HttpConnectionContext extends HttpConnectionContext(Negotiated) {
   /** Java API */
   def getInstance() = this

akka-http-core/src/test/scala/akka/http/javadsl/ConnectHttpSpec.scala

@@ -99,5 +99,10 @@ class ConnectHttpSpec extends WordSpec with Matchers with BeforeAndAfterAll {
       }
       ex.getMessage should include("non https scheme!")
     }
+    "connect toHost HTTP/2 only" in {
+      val connect = ConnectHttp.toHost("http://127.0.0.1", 8080, UseHttp2.always)
+      connect.effectiveConnectionContext(httpsContext).http2 should equal(UseHttp2.always)
+    }
+
   }
 }