Integrate retry mechanism

[djomaa]

Fixes #75
Now if audit fails due to npm registry, it's repeated up to 5 times.

Probably, it would be cool to create parameters for retry delay and retry max attempts.

[quinnturner]

Thank you for your submission! I have outlined a few things to fix in my first pass.

As for the vulnerabilities blocking this, #83 should be merged. Once it is merged, we can merge master into your branch so that CircleCI registers the updated dependencies (to be addressed in #69).

[quinnturner]

I agree that the retry attempt should be configurable. Perhaps the following specification?

Arg: none
Alias: --retry-count
Description: The number of attempts audit-ci calls an unavailable registry before failing (default 5)

Placing this ^ after --registry in the various README options.

Config file spec:
"retry-count": // [Optional] defaults 5

Also, we should consider documenting this behaviour in the README.

If the registry's service is unavailable, audit-ci will re-run 5 times before failing unless otherwise specified with --retry-count. This behaviour has been noted in #75.

[djomaa]

@quinnturner all is ready.

I also changed audit start flow for the availability of the mechanism in tests

[quinnturner]

Created djomaa#1 for some minor fixes along with a git merge master.

It would be a nice-to-have having a test that fails at first due to a 503 then passes. However, it's okay if that is added later.