Add graceful error recovery

[gregelin]

Story

As a user, I don't want issue-packs to fail silently. I would like the program to return a result even if there was a problem. If possible, I would like to use familiar error codes and messages.

More info

Here's my guess at possible errors:

• [ ] Time out talking to Jira or GitHub, etc
• [ ] Authentication error
• [ ] Unable to find issue pack yaml file
• [ ] Unable to parse issue pack yaml file
• [ ] Issue tracker returned unexpected error
• [ ] Only some of the issues were added
• [ ] Targeted Jira endpoint does not exist
• [ ] Targeted Jira project identifier does not exist
• [ ] Unexpected error

As per @leedavidr via email regarding brittleness of error recovery:

On Dec 27, 2016, at 9:54 AM, David Lee david.lee@kastling.com wrote:

Hmm

Should be not bad, I worked on making it better last time. Improved error messages and status when partial fail as well.

Yesterday i worked on validation error messages as well

I didnt try the timeout error scenario but havent seen them when I was testing