Utils_test: Migration enhancements

Fix following problems:
1.Initialize self.params for HostStress class.
2.Use stress_args instead of stress_arg for Stress relative classes.
3.Support to edit control file in run_autotest function.
For example:
```
job.run_test("stress")
```
To
```
job.run_test("stress", args="--cpu 2 xxx", other="xxx")
```