Test: Fix how packaging test generates expected plugins

qa/vagrant/build.gradle

@@ -19,12 +19,23 @@
 
 apply plugin: 'elasticsearch.vagrant'
 
-dependencies {
-  // Collect all the plugins
-  for (Project subproj : project.rootProject.subprojects) {
-    if (subproj.path.startsWith(':plugins:')) {
+List<String> plugins = []
+for (Project subproj : project.rootProject.subprojects) {
+  if (subproj.path.startsWith(':plugins:')) {
+    // add plugin as a dep
+    dependencies {
       bats project(path: "${subproj.path}", configuration: 'zip')
     }
+    plugins.add(subproj.name)
+  }
+}
+plugins = plugins.toSorted()
+
+setupBats {
+  doFirst {
+    File expectedPlugins = file('build/plugins/expected')
+    expectedPlugins.parentFile.mkdirs()
+    expectedPlugins.setText(plugins.join('\n'), 'UTF-8')
   }
 }
 

qa/vagrant/src/test/resources/packaging/utils/plugins.bash

@@ -173,8 +173,6 @@ install_and_check_plugin() {
 # $2 description of the source of the plugin list
 compare_plugins_list() {
     cat $1 | sort > /tmp/plugins
-    ls /elasticsearch/plugins/*/build.gradle | cut -d '/' -f 4 |
-        sort > /tmp/expected
     echo "Checking plugins from $2 (<) against expected plugins (>):"
-    diff /tmp/expected /tmp/plugins
+    diff -w /elasticsearch/qa/vagrant/build/plugins/expected /tmp/plugins
 }