Script to rolling-start Nomulus (#888)

* Script to rolling-start Nomulus

Add a script to restart Nomulus non-disruptively. This can be used after
a configuration change to external resources (e.g.,  Cloud SQL
credential) to make Nomulus pick up the latest config.

Also added proper support to paging based List api methods, replacing the
current hack that forces the server to return everything in one response.
The List method for instances has a lower limit on page size than others
which is not sufficient for our project.

release/rollback/steps.py

@@ -122,6 +122,24 @@ def direct_service_traffic_to_version(
          '--quiet', f'--splits={version.version_id}=1', '--project', project))
 
 
+@dataclasses.dataclass(frozen=True)
+class KillNomulusInstance(RollbackStep):
+    """Step that kills a Nomulus VM instance."""
+    instance_name: str
+
+
+# yapf: disable
+def kill_nomulus_instance(project: str,
+                          version: common.VersionKey,
+                          instance_name: str) -> KillNomulusInstance:
+    # yapf: enable
+    return KillNomulusInstance(
+        'Delete one VM instance.',
+        ('gcloud', 'app', 'instances', 'delete', instance_name, '--quiet',
+         '--user-output-enabled=false', '--service', version.service_id,
+         '--version', version.version_id, '--project', project), instance_name)
+
+
 @dataclasses.dataclass(frozen=True)
 class _UpdateDeployTag(RollbackStep):
     """Updates the deployment tag on GCS."""