Add ability to get a shell in a failing WDL container

[unito-bot]

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When a WDL job fails, I want to be able to inspect the environment it was working in.

I should be able to use toil debug-job to get a shell in the container that a failing WDL job is going to run in, or that it has run in. It should have all the input files available, and also the binaries that the WDL command is going to/has tried to run.

┆Issue is synchronized with this Jira Story ┆Epic: Improve debugging experience ┆Issue Number: TOIL-1512

[unito-bot]

➤ Adam Novak commented:

This might involve making the job run a sleep instead of the real command when you flip a switch on toil debug-job.