Show a more detailed error message when hitting GitHub rate limits

[pditommaso]

GitHub public repositories have a very low rate limits. See https://developer.github.com/v3/#rate-limiting

When trying to download a repository for which the user reached the access rate limit, Nextflow reports that the repository does not exists.

Cannot find cbcrg/piper-nf pipeline -- Make sure exists a GitHub repository at https://github.com/cbcrg/piper-nf

This is confusing the user. It should provide a more detailed error message suggesting to enter its credentials.

HTTP/1.1 403 Forbidden
Access-Control-Allow-Credentials: true
Access-Control-Allow-Origin: *
Access-Control-Expose-Headers: ETag, Link, X-GitHub-OTP, X-RateLimit-Limit, X-RateLimit-Remaining, X-RateLimit-Reset, X-OAuth-Scopes, X-Accepted-OAuth-Scopes, X-Poll-Interval
Content-Encoding: gzip
Content-Security-Policy: default-src 'none'
Content-Type: application/json; charset=utf-8
Date: Tue, 09 Sep 2014 12:41:08 GMT
Server: GitHub.com
Status: 403 Forbidden
Strict-Transport-Security: max-age=31536000; includeSubdomains; preload
Transfer-Encoding: chunked
X-Content-Type-Options: nosniff
X-Frame-Options: deny
X-GitHub-Media-Type: github.v3
X-GitHub-Request-Id: 545842C2:592E:19837FF:540EF564
X-RateLimit-Limit: 60
X-RateLimit-Remaining: 0
X-RateLimit-Reset: 1410267414
X-XSS-Protection: 1; mode=block

{
    "documentation_url": "https://developer.github.com/v3/#rate-limiting", 
    "message": "API rate limit exceeded for 84.88.66.194. (But here's the good news: Authenticated requests get a higher rate limit. Check out the documentation for more details.)"
}