Restore original System Properties after tests

Many registry tools tests modify system properties but do not
restore them to original state. These tests must be isolated
from each other and cannot share the same test execution process.

This has a huge impact on test performance under Gradle, which
seems to have higher process startup overhead. Current Gradle
test config has to set 'forEvery' to 1, i.e., every test class
must be run in a freshly started process.

This change significantly reduces the number of tests that need
isolation, making it easier to optimize test config for the
remaining tests.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=221350284

javatests/google/registry/tools/DefaultRequestFactoryModuleTest.java

@@ -21,7 +21,9 @@ import com.google.api.client.http.HttpRequest;
 import com.google.api.client.http.HttpRequestFactory;
 import com.google.api.client.http.HttpRequestInitializer;
 import google.registry.config.RegistryConfig;
+import google.registry.testing.SystemPropertyRule;
 import org.junit.Before;
+import org.junit.Rule;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.junit.runners.JUnit4;
@@ -40,11 +42,13 @@ public class DefaultRequestFactoryModuleTest {
         }
       });
 
+  @Rule public final SystemPropertyRule systemPropertyRule = new SystemPropertyRule();
+
   DefaultRequestFactoryModule module = new DefaultRequestFactoryModule();
 
   @Before
   public void setUp() {
-    RegistryToolEnvironment.UNITTEST.setup();
+    RegistryToolEnvironment.UNITTEST.setup(systemPropertyRule);
   }
 
   @Test