build(java): fix nightly integration test config to run integrations (#465)

This was only running the units.

Author: chingor13

synthtool/gcp/templates/java_library/.kokoro/nightly/integration.cfg

@@ -6,11 +6,26 @@ env_vars: {
   value: "gcr.io/cloud-devrel-kokoro-resources/java8"
 }
 
+env_vars: {
+  key: "JOB_TYPE"
+  value: "integration"
+}
+
+env_vars: {
+  key: "GCLOUD_PROJECT"
+  value: "gcloud-devel"
+}
+
 env_vars: {
   key: "ENABLE_BUILD_COP"
   value: "true"
 }
 
+env_vars: {
+    key: "GOOGLE_APPLICATION_CREDENTIALS"
+    value: "keystore/73713_java_it_service_account"
+}
+
 before_action {
   fetch_keystore {
     keystore_resource {