build: use span-cloud-testing for integration tests (googleapis#1994)

Author: olavloite

.kokoro/build.sh

@@ -76,6 +76,8 @@ integration)
       -DtrimStackTrace=false \
       -Dclirr.skip=true \
       -Denforcer.skip=true \
+      -Dspanner.testenv.instance=projects/span-cloud-testing/instances/java-client-integration-test \
+      -Dspanner.gce.config.project_id=span-cloud-testing \
       -fae \
       verify
     RETURN_CODE=$?

.kokoro/presubmit/integration.cfg

@@ -11,24 +11,13 @@ env_vars: {
   value: "integration"
 }
 
-# TODO: remove this after we've migrated all tests and scripts
-env_vars: {
-  key: "GCLOUD_PROJECT"
-  value: "gcloud-devel"
-}
-
-env_vars: {
-  key: "GOOGLE_CLOUD_PROJECT"
-  value: "gcloud-devel"
-}
-
 env_vars: {
   key: "GOOGLE_APPLICATION_CREDENTIALS"
-  value: "secret_manager/java-it-service-account"
+  value: "secret_manager/java-client-testing"
 }
 
 env_vars: {
   key: "SECRET_MANAGER_KEYS"
-  value: "java-it-service-account"
+  value: "java-client-testing"
 }