Improve port and process management

Add isBindableByProc which uses /proc/net to search available port.
Change userPorts-range from [49152..65535] to [5001..32767].
 ([49152..65535] is os-port-searching area.)
Add cleanUpProcesses which stops process-groups when test is finished.
Add runSB and withSandbox funtions for unit-test
Add comment for userPorts