Port build to SBT 1.x (#23850)

* Port build to SBT 1.x

* Fix multinode tests, always enable genjavadoc bootstrap

project/VersionGenerator.scala

@@ -0,0 +1,33 @@
+/**
+ * Copyright (C) 2016-2017 Lightbend Inc. <http://www.lightbend.com>
+ */
+package akka
+
+import sbt._
+import sbt.Keys._
+
+/**
+ * Generate version.conf and akka/Version.scala files based on the version setting.
+ */
+object VersionGenerator {
+
+  val settings: Seq[Setting[_]] = inConfig(Compile)(Seq(
+    resourceGenerators += generateVersion(resourceManaged, _ / "version.conf",
+      """|akka.version = "%s"
+         |"""),
+    sourceGenerators += generateVersion(sourceManaged, _ / "akka" / "Version.scala",
+      """|package akka
+         |
+         |object Version {
+         |  val current: String = "%s"
+         |}
+         |""")))
+
+  def generateVersion(dir: SettingKey[File], locate: File ⇒ File, template: String) = Def.task[Seq[File]] {
+    val file = locate(dir.value)
+    val content = template.stripMargin.format(version.value)
+    if (!file.exists || IO.read(file) != content) IO.write(file, content)
+    Seq(file)
+  }
+
+}