Fix Gradle configuration cache issue in DockerBuildImage tasks

Remove script-level mutable collection reference from DockerBuildImage
task actions which is not compatible with Gradle configuration cache.
Instead, collect image names at configuration time and pass them
directly to the pushMatrix task.

Author: trask

smoke-tests/images/servlet/build.gradle.kts

@@ -177,8 +177,6 @@ val targets = mapOf(
   ),
 )
 
-val matrix = mutableListOf<String>()
-
 tasks {
   val buildLinuxTestImages by registering {
     group = "build"
@@ -190,17 +188,17 @@ tasks {
     description = "Builds all Windows Docker images for the test matrix"
   }
 
+  val linuxImages = createDockerTasks(buildLinuxTestImages, false)
+  val windowsImages = createDockerTasks(buildWindowsTestImages, true)
+
   val pushMatrix by registering(DockerPushImage::class) {
     mustRunAfter(buildLinuxTestImages)
     mustRunAfter(buildWindowsTestImages)
     group = "publishing"
     description = "Push all Docker images for the test matrix"
-    images.set(matrix)
+    images.set(linuxImages + windowsImages)
   }
 
-  createDockerTasks(buildLinuxTestImages, false)
-  createDockerTasks(buildWindowsTestImages, true)
-
   val printSmokeTestsConfigurations by registering {
     doFirst {
       for ((server, matrices) in targets) {
@@ -357,9 +355,6 @@ fun configureImage(
     images.add(image)
     dockerFile.set(File(dockerWorkingDir.get().asFile, dockerFileName))
     buildArgs.set(extraArgs + mapOf("jdk" to jdk, "vm" to vm, "version" to version, "jdkImageName" to jdkImageName, "jdkImageHash" to jdkImageHash, "imageHash" to serverImageHash))
-    doLast {
-      matrix.add(image)
-    }
   }
 
   parentTask.configure {
@@ -368,7 +363,7 @@ fun configureImage(
   return image
 }
 
-fun createDockerTasks(parentTask: TaskProvider<out Task>, isWindows: Boolean) {
+fun createDockerTasks(parentTask: TaskProvider<out Task>, isWindows: Boolean): Set<String> {
   val resultImages = mutableSetOf<String>()
   for ((server, matrices) in targets) {
     val smokeTestServer = findProperty("smokeTestServer")
@@ -397,4 +392,5 @@ fun createDockerTasks(parentTask: TaskProvider<out Task>, isWindows: Boolean) {
       }
     }
   }
+  return resultImages
 }