Display composer validation output

[defunctl]

Description

Currently, if composer validate fails, you don't actually know why. This displays the error message.

Motivation and context

Not an exact fix for this, but at least it would tell the user what went wrong: #250

How has this been tested?

I ran it in my private GitHub repo.

Before:

After:

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

PR checklist

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING.md document.
• I have added tests to cover my changes.

[ramsey]

Please check the test failures. I can help with the Bats tests, if needed—just let me know.