[VC-35738] Remove os.Exit from the logs module

[wallrj]

Instead of calling os.exit directly after parsing and finding an error in the logging flags, the error is now returned and handled the same way as errors that come from the Run function....they are logged using structured logging and the logs are flushed before the process exits.

I've adjusted the logs tests accordingly and modified them so that the log flag parsing and error handling in the tests matches the behaviour of the actual command.

Before:

$ ./preflight agent --logging-format=foo
Error in logging configuration: format: Invalid value: "foo": Unsupported log format

$ echo $?
2

After:

$ ./preflight agent --logging-format=foo
E1107 13:41:31.063915  281828 root.go:51] "Exiting due to error" err="Error in logging configuration: format: Invalid value: \"foo\": Unsupported log format" exit-code=1

$ echo $?
1

[wallrj]

Returning the error here means that the error can be logged in the same format as all the other errors that are returned by the command.

[wallrj]

These changes are intended to make the logs test fixture parse the flags and behave the same way as Cobra.

• --help / -h results in stdout and exit code 0
• Unrecognized flags result in an error which is logged to stderr with exit code 1

[maelvls]

Thanks for the extra context. I think it would be worth adding a comment above to keep that in mind in the future. I'm already imagining myself in a year: why do we do this weird dance with the exit codes in the test code?

[wallrj]

I'll merge this now and add the comment in one of the followup PRS.

[maelvls]

This sounds like a good change. I haven't tested the change manually nor have I run the automated tests, I trust you.