Add detection logging messages at info level

[anthonydahanne]

Log messages were checked during testing

=== RUN   TestUnit/liberty/Detect/fails_if_a_Main-Class_is_present
SKIPPED: Detected build source is null

Summary

This PR adds additional logging when Detect returns false for this buildpack. This is to provide more information about why the detection failed for this buildpack when verbose/debug logging is enabled.

As of lifecycle v1.16.0, if the detect phase fails as a whole, log messages are printed at info level by default, without the need for the verbose flag.

Use Cases

A pack build command with the --verbose flag set will show these log statement if detection fails. If Detect succeeds, the output is not shown unless --verbose is set.

Checklist

• I have viewed, signed, and submitted the Contributor License Agreement.
• I have linked issue(s) that this PR should close using keywords or the Github UI (See docs)
• I have added an integration test, if necessary.
• I have reviewed the styleguide for guidance on my code quality.
• I'm happy with the commit history on this PR (I have rebased/squashed as needed).