Add error messages to report.csv

[jeremyfowers]

Current behavior:

• Error messages are logged into *_log.txt files that correspond to the Stages and Runtimes that execute.
• turnkey cache report produces a report.csv file that includes status (e.g., error), but does not provide a convenient way to find out what the error was.
• Users are responsible for acquiring the logs and correlating them with the report to learn more about each error.

Proposed solution: if a function fails, include the contents of its logfile in the report CSV file

Potential problem: this might make the CSV file absurdly large on some datasets. Not sure if that is a problem or not, since we could handle a 1 GB CSV file if needed. Perhaps this could be mitigated by only storing the last 10 lines of the log into the CSV.

cc @danielholanda @ramkrishna2910