Enhance the test for forbidden Schema changes (#815)

* Enhance the test for forbidden Schema changes

Current test is git-based. It is difficult to maintain and does not
catch out-of-order version numbers. It is also more aggressive than
necessary, failing on changes to submitted scripts that have not been
deployed yet.

The new test starts a database, deploys the current schema to it,
then deploys the set of Flyway scripts in this repository to the database.

integration/run_compatibility_tests.sh

@@ -79,6 +79,8 @@ function runTest() {
   echo "Running test with -Pnomulus_version=${nomulus_version}" \
       "-Pschema_version=${schema_version}"
 
+  # The https scheme in the Maven repo URL below is required for Kokoro. See
+  # ./run_schema_check.sh for more information.
   (cd ${SCRIPT_DIR}/..; \
       ./gradlew :integration:sqlIntegrationTest \
           -PdevProject=${dev_project} \