Enable dynamic debugging in Weston

Currently, if we want to enable weston_debug_v1 debugging interface, we have to stop weston and run it again with --debug option. And there is no way to disable debug protocol once it is enabled. After merging these changes, we will be able to enable and disable weston_debug_v1 interface dynamically without stopping weston. For that, we have to pass the SIGURG signal to the weston process using the below command:

kill -23 weston_process_id

If the debug protocol is enabled, this command will disable it. If it is disabled, then it will enable the debug protocol.