Add 'gerrit set-topic' SSH command

Currently the only way to set the topic is through the REST API,
however this is a bit annoying if you don't want to use the REST API.
It's desirable to also have an SSH command that covers this use case.

Change-Id: I6686e64a788365bd252df69ae5b3ec9d65aaf068

javatests/com/google/gerrit/acceptance/ssh/SshCommandsIT.java

@@ -74,6 +74,7 @@ public class SshCommandsIT extends AbstractDaemonTest {
           "set-project",
           "set-project-parent",
           "set-reviewers",
+          "set-topic",
           "stream-events",
           "test-submit");