When a process fails, check if the output is enabled

With the recent addition of the ability to disable the output, it was
not taken into account within the `ProcessFailedException`.

So, if the output was indeed disabled, and the process returns an
error (i.e via a `mustRun`) we could have another LogicException which
is not expected.
bug #10530 [Process] Do not show output in FailedException if it was disabled (Taluu)

This PR was merged into the 2.5-dev branch.

Discussion
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[Process] Do not show output in FailedException if it was disabled

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | ~
| License       | MIT
| Doc PR        | ~

With the recent addition of the ability to disable the output, it was not taken into account within the `ProcessFailedException`.

So, if the output was indeed disabled, and the process returns an error and triggers a `ProcessFailedException` exception (i.e via a mustRun), we could have another LogicException which is not  expected.

Commits
-------

849703a When a process fails, check if the output is enabled