create a test that fails to demonstrate issue #75

[ryangardner]

Note: in its current form, this test fails... I haven't worked on a fix for it, but figured an IT that failed might make it easier to fix the issue reported in #75

[ryangardner]

Hmm... nevermind. this test doesn't demonstrate this issue yet. I'll try to improve it so it does.

[ryangardner]

This latest PR also adds a simple fix for the issue identified... the test metadata method tries to copy everything from the docker info directory over - if that directory is used for something else and has folders in it, the copy will fail.

It seems like only copying the set of expected files over would be a better behavior, because it's hard to detect if someone is putting files in that directory that shouldn't be there - but if there is a directory there in this PR it will be detected and a suggestion on how to configure the plugin will be logged at the warning level

[mattnworb]

Thanks for the PR and for aiming to reproduce this in a test case.

I'd prefer if this issue was addressed by validating at the start of the plugin execution that contextDirectory and dockerInfoDirectory were not colliding or overlapping, as I think that would probably cause additional headaches or weird behavior beyond the writeTestMetadata exception.