Move to using Android Gradle Plugin 3.0.0-alpha4

Bug: 62578429
Test: ./gradlew buildOnServer
Change-Id: I354fb8d4edf8eacc75117f4cff13184865fe6b22
diff --git a/buildSrc/init.gradle b/buildSrc/init.gradle
index 50f2890..eb1c001 100644
--- a/buildSrc/init.gradle
+++ b/buildSrc/init.gradle
@@ -301,9 +301,10 @@
                 task.doLast {
                     def source = testApk ? project.android.sourceSets.androidTest
                             : project.android.sourceSets.main
-                    if (task.hasProperty("outputFile") && !source.java.sourceFiles.isEmpty()) {
+                    if (task.hasProperty("outputDirectory") && !source.java.sourceFiles.isEmpty()) {
                         copy {
-                            from(task.outputFile)
+                            from(task.outputDirectory)
+                            include '*.apk'
                             into(rootProject.ext.testApkDistOut)
                             rename { String fileName ->
                                 // multiple modules may have the same name so prefix the name with