Start sending heartbeats immediately when joining, see #2249

* Keep track of joins that are in progress in State.joinInProgress,
  with Deadline
* Add test that fails without this feature

akka-cluster/src/multi-jvm/scala/akka/cluster/JoinInProgressSpec.scala

@@ -0,0 +1,65 @@
+/**
+ *  Copyright (C) 2009-2012 Typesafe Inc. <http://www.typesafe.com>
+ */
+package akka.cluster
+
+import com.typesafe.config.ConfigFactory
+import org.scalatest.BeforeAndAfter
+import akka.remote.testkit.MultiNodeConfig
+import akka.remote.testkit.MultiNodeSpec
+import akka.testkit._
+import akka.util.duration._
+import akka.util.Deadline
+
+object JoinInProgressMultiJvmSpec extends MultiNodeConfig {
+  val first = role("first")
+  val second = role("second")
+
+  commonConfig(
+    debugConfig(on = false)
+      .withFallback(ConfigFactory.parseString("""
+          akka.cluster {
+            # simulate delay in gossip by turning it off
+            gossip-interval = 300 s
+            failure-detector {
+              threshold = 4
+              acceptable-heartbeat-pause = 1 second
+            }
+          }""") // increase the leader action task interval
+        .withFallback(MultiNodeClusterSpec.clusterConfig)))
+}
+
+class JoinInProgressMultiJvmNode1 extends JoinInProgressSpec with AccrualFailureDetectorStrategy
+class JoinInProgressMultiJvmNode2 extends JoinInProgressSpec with AccrualFailureDetectorStrategy
+
+abstract class JoinInProgressSpec
+  extends MultiNodeSpec(JoinInProgressMultiJvmSpec)
+  with MultiNodeClusterSpec {
+
+  import JoinInProgressMultiJvmSpec._
+
+  "A cluster node" must {
+    "send heartbeats immediately when joining to avoid false failure detection due to delayed gossip" taggedAs LongRunningTest in {
+
+      runOn(first) {
+        startClusterNode()
+      }
+
+      enterBarrier("first-started")
+
+      runOn(second) {
+        cluster.join(first)
+      }
+
+      runOn(first) {
+        val until = Deadline.now + 5.seconds
+        while (!until.isOverdue) {
+          200.millis.sleep
+          cluster.failureDetector.isAvailable(second) must be(true)
+        }
+      }
+
+      enterBarrier("after")
+    }
+  }
+}