Implemented ssh command create-group

Often, when creating a new gerrit project a gerrit admin
needs to create a new project owner group and setup an initial
set of group members. This was only possible from gerrit's Web UI
and was a realtively slow process compared to the easiness of
creating the project using the create-project ssh command.

This command makes it possible to create a new group, assign
group members, owner group and description via ssh.

Bug: issue 313
Change-Id: I9fbc013bd5e596f0b23e411ee0cc72d5f67b5f39
Signed-off-by: Sasa Zivkov <sasa.zivkov@sap.com>

gerrit-sshd/src/main/java/com/google/gerrit/sshd/BaseCommand.java

@@ -343,6 +343,10 @@ public abstract class BaseCommand implements Command {
     }
   }
 
+  protected UnloggedFailure die(String msg) {
+    return new UnloggedFailure(1, "fatal: " + msg);
+  }
+
   private final class TaskThunk implements CancelableRunnable, ProjectRunnable {
     private final CommandRunnable thunk;
     private final Context context;