utils_test.HostStress: Set default value for params.

Signed-off-by: Yu Mingfei <yumingfei@cn.fujitsu.com>
utils_test: Pass correct args to control file.

Signed-off-by: Yu Mingfei <yumingfei@cn.fujitsu.com>
utils_test.run_autotest: Support to pass args for control.

Signed-off-by: Yu Mingfei <yumingfei@cn.fujitsu.com>
Merge pull request #1664 from yumingfei/migration_enhancements

Utils_test: Migration enhancements