[Misc] Polish the benchmark scripts

[Jeffwan]

Pull Request Description

1. Rename some variables for self-explaination and rename the output files by removing empty lines
2. mkdir the —output-dir if it doesn’t exist, and add output folder name to .gitignore
3. Change the triple quote markdown to single quote in single line.
4. Reformat all generator codes
5. Change the logging level
6. Add duration check for tracing files and fallback to right duration if it's over the limit

Related Issues

Resolves: #523

Important: Before submitting, please complete the description above and review the checklist below.

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[Jeffwan]

@happyandslow do you get a chance to look at this change?