Abort websocket server listen() retry on shutdown
Abort websocket server listen() retry on shutdown

This allows the server to shut down via SIGINT or SIGTERM during its listen() retry loop.

SNU-Sigma/rosbridge_suite,RobotWebTools/rosbridge_suite,vladrotea/rosbridge_suite,SNU-Sigma/rosbridge_suite,vladrotea/rosbridge_suite,SNU-Sigma/rosbridge_suite,vladrotea/rosbridge_suite,SNU-Sigma/rosbridge_suite