[merge] Cleanup error tests

[John Arbash Meinel]

This patch has 2 changes:

1) Moves my old error tests into the right place. I had misunderstood
the original TestErrors class, and created a new one to do the same thing.

2) Adds a test for test_install_failed(), and fixes InstallFailed so
that it works if given None, and fixes the " ,".join() to be ", ".join()

It is a small cleanup.

The weirdest part, is because the amount of code I moved was large, it
actually shows up as moving the code I didn't touch. Certainly I could
have reached the same result by moving the other code, and then deleting
the class definition line.

John
=:->
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