Rewrite run_combination_test to internally execute run_multi_test

[kmaehashi]

This will make us easy to reproduce combination (daily shuffle) test failures in CI environment.

[kmaehashi]

Maybe fixed in the latest version? Let me check.

[kmaehashi]

This is still an issue, I couldn't reproduce the same combination in my local environment.

[kmaehashi]

This is still an issue, I couldn't reproduce the same combination in my local environment.

For now, we can workaround this issue by using py2 (which is used by Jenkins master) to reproduce the same combination as the Jenkins.