utils_test: Add class for control stress tool.

Signed-off-by: Yu Mingfei <yumingfei@cn.fujitsu.com>
utils_test: Support loading stress for test.

Signed-off-by: Yu Mingfei <yumingfei@cn.fujitsu.com>
Merge pull request #1527 from yumingfei/control_stress

utils_test: Add class for controlling stress tool.