Add SetNumInstancesCommand in Nomulus tool to adjust the number of instances

for a given service and version at runtime.

Note that this CL only supports the adjustment for a given service and version. I will add another functionality to let this command be able to detect all non-live versions automatically and apply the adjustment.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=221092001

java/google/registry/tools/SetNumInstancesCommand.java

@@ -0,0 +1,66 @@
+// Copyright 2018 The Nomulus Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package google.registry.tools;
+
+import static com.google.common.base.Preconditions.checkArgument;
+
+import com.beust.jcommander.Parameter;
+import com.beust.jcommander.Parameters;
+import com.google.common.flogger.FluentLogger;
+import google.registry.util.AppEngineServiceUtils;
+import javax.inject.Inject;
+
+/** A command to set the number of instances for an App Engine service. */
+@Parameters(
+    separators = " =",
+    commandDescription =
+        "Set the number of instances for a given service and version. "
+            + "Note that this command only works for manual scaling service.")
+final class SetNumInstancesCommand implements CommandWithRemoteApi {
+
+  private static final FluentLogger logger = FluentLogger.forEnclosingClass();
+
+  @Parameter(
+      names = "--service",
+      description = "Name of the App Engine service, e.g., default.",
+      required = true)
+  private String service;
+
+  @Parameter(
+      names = "--version",
+      description = "Name of the service's version, e.g., canary.",
+      required = true)
+  private String version;
+
+  @Parameter(
+      names = "--numInstances",
+      description = "The new number of instances for the version.",
+      required = true)
+  private Long numInstances;
+
+  @Inject AppEngineServiceUtils appEngineServiceUtils;
+
+  @Override
+  public void run() throws Exception {
+    checkArgument(!service.isEmpty(), "Service must be specified");
+    checkArgument(!version.isEmpty(), "Version must be specified");
+    checkArgument(numInstances > 0, "Number of instances must be greater than zero");
+
+    appEngineServiceUtils.setNumInstances(service, version, numInstances);
+    logger.atInfo().log(
+        "Successfully set version %s of service %s to %d instances.",
+        version, service, numInstances);
+  }
+}