veyron2/opts.go: Add DebugAuthorizerOpt

Add an option to set the authorizer to control access to internal
debug objects. By default, the authorizer is nil, which only gives
access to principals with the right blessings.

Change-Id: I1b0fbbfe1f9a9ae1370ea2151224495617d46776
diff --git a/runtimes/google/ipc/server.go b/runtimes/google/ipc/server.go
index 4764944..ae507af 100644
--- a/runtimes/google/ipc/server.go
+++ b/runtimes/google/ipc/server.go
@@ -52,6 +52,7 @@
 	addressChooser   veyron2.AddressChooser
 	servesMountTable bool
 	roamingOpt       veyron2.RoamingPublisherOpt
+	debugAuthorizer  security.Authorizer
 	// TODO(cnicolaou): add roaming stats to ipcStats
 	stats *ipcStats // stats for this server.
 }
@@ -86,6 +87,8 @@
 			s.listenerOpts = append(s.listenerOpts, opt)
 		case veyron2.ServesMountTableOpt:
 			s.servesMountTable = bool(opt)
+		case veyron2.DebugAuthorizerOpt:
+			s.debugAuthorizer = security.Authorizer(opt)
 		}
 	}
 	return s, nil