CLI raising should impact exit code

[christhekeele]

Expectation:

With the raise: true config set, when running mix doctor, when my Doctor validation fails, I'd expect the task to return a non-zero status code.

Observed:

Failing and non-failing runs always return a 0 exit code.

Implementation:

One neat thing I've seen such tools do is encode the number of failures in the returned status code, so bash CI scripts can externally permit/enforce a certain number of failures.