veyron/services/mgmt/debug: Use callback for logdir

At the time debug.NewDispatcher() is called, the vlog library hasn't
been initialized yet. So, instead of trying to figure out the correct
log dir at that time, use a callback function that will be called after
the runtime initialization has completed.

Change-Id: Ieed799b4b3b0dfd6e53b04b79ebe51e60c0adcf4
diff --git a/profiles/roaming/roaminginit.go b/profiles/roaming/roaminginit.go
index 8b9eb01..3e6de0b 100644
--- a/profiles/roaming/roaminginit.go
+++ b/profiles/roaming/roaminginit.go
@@ -57,7 +57,7 @@
 		Addrs: ipc.ListenAddrs(lf.Addrs),
 		Proxy: lf.ListenProxy,
 	}
-	reservedDispatcher := debug.NewDispatcher(vlog.Log.LogDir(), sflag.NewAuthorizerOrDie())
+	reservedDispatcher := debug.NewDispatcher(vlog.Log.LogDir, sflag.NewAuthorizerOrDie())
 
 	ac := appcycle.New()