Adds get_unused_port method to helper and applies it in serve_file 5909
Adds get_unused_port method to helper and applies it in serve_file 5909

CartoDB/cartodb,splashblot/dronedb,bloomberg/cartodb,splashblot/dronedb,splashblot/dronedb,bloomberg/cartodb,CartoDB/cartodb,bloomberg/cartodb,codeandtheory/cartodb,codeandtheory/cartodb,codeandtheory/cartodb,bloomberg/cartodb,bloomberg/cartodb,splashblot/dronedb,codeandtheory/cartodb,codeandtheory/cartodb,CartoDB/cartodb,CartoDB/cartodb,splashblot/dronedb,CartoDB/cartodb