Save subruns information of hyperrun

[dachengx]

What is the problem / what does the code in this PR do

Can you briefly describe how it works?

Can you give a minimal working example (or illustrate with a figure)?

Please include the following if applicable:

• Update the docstring(s)
• Update the documentation
• Tests to check the (new) code is working as desired.
• Does it solve one of the open issues on github?

Please make sure that all automated tests have passed before asking for a review (you can save the PR as a draft otherwise).

[coveralls]

coverage: 89.802% (+0.2%) from 89.607% when pulling 3268c8f08f3cfd951c99f633c6d09019f05d62da on save_hyperrun_subruns into 66e974b63451c308f965a63937883aed18603b3b on master.