Mvnd should fail is extension cannot be loaded

[gnodet]

          > @gnodet If you run this PR locally:

• it will pass ok, but
• maven-conf-ignore-ext IT is wrong: maven.conf where ignore is, is not observed by mvnd. Also local repository will show that extension foo:bar is attempted to resolve, but naturally unsuccessfully
• this means that mvnd happily goes along instead to fail (as it failed to resolve the extension)

Any idea?

Yes, the problem is here:

• maven-mvnd/daemon-m40/src/main/java/org/apache/maven/cli/DaemonMavenCli.java

  Line 699 in dc4179f

  slf4jLogger.warn("Failed to load extensions descriptor {}: {}", extensions, e.getMessage());

• maven-mvnd/daemon-m39/src/main/java/org/apache/maven/cli/DaemonMavenCli.java

  Line 615 in dc4179f

  slf4jLogger.warn("Failed to load extensions descriptor {}: {}", extensions, e.getMessage());

  
  A failure to resolve the extension simply prints a warning and ignore.... That should be fixed.

Originally posted by @gnodet in #953 (comment)