fawkes should be able to fail if a plugin fails to load

[vmatare]

Now that we have automated tests, a fawkes "testing mode" would be helpful. Currently, fawkes is designed to run as robustly as possible, i.e. to die on exceptions as rarely as possible. However on automated tests, we want the binary to fail executing due to whatever goes wrong. Failed plugin load is sort of a low-hanging fruit here that should cover many error conditions.

[stale]

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