add speculative_retry to the output file config.json, so that we can know which method we are using

add speculative_retry to the output file config.json, so that we can know which method we are using

BUG=

[cuteliaoliao, 2017-10-06 13:34:56]

Works well. Clear to know the using method. Good job!

[mumuzuge, 2017-10-06 13:34:57]

We can know that it is using the method speculative retries when reading the
output.

[Jiangfeng, 2017-10-07 15:59:25]

add speculative retry parameter to config.json in output files. It provides
convenience when analyzing the output results.