refactor parallel code

openos/time.lua

@@ -0,0 +1,18 @@
+local computer = require('openos.computer')
+local sh = require('openos.sh')
+
+local real_before, cpu_before = computer.uptime(), os.clock()
+local cmd_result = 0
+if ... then
+  sh.execute(nil, ...) 
+  cmd_result = sh.getLastExitCode()
+end
+local real_after, cpu_after = computer.uptime(), os.clock()
+
+local real_diff = real_after - real_before
+local cpu_diff = cpu_after - cpu_before
+
+print(string.format('real%5dm%.3fs', math.floor(real_diff/60), real_diff%60))
+print(string.format('cpu %5dm%.3fs', math.floor(cpu_diff/60), cpu_diff%60))
+
+return cmd_result