improve error feedback

[sverweij]

Description

If puppeteer/ chrome headless fails, currently mscgenjs-cli returns the unhelpful Invalid non-string/buffer chunk error message instead of the root cause of the error. With this PR mscgenjs-cli will report the root cause of the error.

Motivation and Context

Not explicitly raised in #21 - but people less tech savvy than the reporter would've been thoroughly befuddled by the generic error message instead of the loud & clear puppeteer message

Failed to launch chrome! spawn /usr/iznogood/bin/chromium ENOENT


TROUBLESHOOTING: https://github.com/GoogleChrome/puppeteer/blob/master/docs/troubleshooting.md

How Has This Been Tested?

Unit & manual tests

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• The code I add will be subject to The GNU General Public License v3 (text), and I'm OK with that.
• The code I've added is my own original work.
• My code follows the code style of this project.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.