Need a means to save temporary generated directories on failure

[ngie-eign]

In the event a test fails, there isn't a means for testers to recover necessary data in order to determine why an issue occurred in all cases.

It would be nice if there was a configurable hook in kyua where a set of arbitrary commands could be executed on cleanup to save a the directories, there was a configuration variable where the directory could be saved, etc...

[jmmv]

My idea for this was to extend kyua debug with an option to keep the contents if desired. E.g. doing kyua debug --workdir=/tmp/foo some-test would force Kyua to use that work directory and not clean it up on exit.

However, I'm not sure that'd be sufficient. Especially because this requires a re-run of the test.

We could go one step further and support something like kyua test --workdir=/tmp/foo, which would cause us to run all tests and only keep work directories for the tests that failed.

In other words: if no --workdir is provided, Kyua picks a temporary directory on its own and makes sure it's fully wiped on exit. If the user provides his own directory, it is not automatically cleaned up for failures. Makes sense?