Fix for command line argument for debugAddr

The `cf_debug_server` parses flag for `-debugAddr="": host:port for serving pprof debugging info`. Since this is using flag it prints under running the gorouter binary as `cf_debug_server` is loaded in main.go.
This does not work as the existing main.go code __only__ calls `cf_debug_server` if DebugAddr is passed as part of config.

This fix uses the config value first and falls back to allow cf_debug_server to use the debugAddr argument. In the case of both missing a cf_debug_server is not started.

I am an Intel employee and should be covered under the existing Intel CLA.