Allow schema-loading from arbitrary url in tests (#374)

* Allow schema-loading from arbitrary url in tests

Server/Schema compatibility tests must be able to load different versions
of the SQL schema. This change allows test runners to override the
schema location using a system property.

Note: due to dependency-locking, we cannot manipulate the dependencies
closure in the build script to load different schema jars. The jars
must not be on the classpath.

core/build.gradle

@@ -660,6 +660,8 @@ task outcastTest(type: FilteringTest) {
 
 // Dedicated test suite for schema-dependent tests.
 task sqlIntegrationTest(type: FilteringTest) {
+  systemProperties project.getProperties().subMap('sql_schema_resource_root')
+
   excludeTestCases = false
   tests = ['google/registry/schema/integration/SqlIntegrationTestSuite.*']
 }