Output of the ISO/IMG build is confusing

The output (stdout, stderr) of our build system is confusing: it mixes status info we echo on purpose (generally, that’s essentially section headings) with the output of whatever tool we run to implement what the section is about. Similarly, when a build fails, it’s hard to tell what’s the reason: the higher-level error message we display on purpose is generally hidden in the middle of lower-level tools output.

If all the instances of echo in our build source code were using the “E: ”, “I: ”, “W: ” prefix convention, such output would be easier to read. More involved solutions could improve this further but let’s first focus on this low-hanging fruit and see how it goes.

(Reporting from a discussion with segfault.)

Related issues

• Related to #15864

Original created by @intrigeri on 16639 (Redmine)