Should nerve consider a 3xx status to be successful?

[Evan Krall]

Context: https://github.com/Yelp/hacheck/pull/4

We discovered one of our services (mistakenly) returning 3xx status codes; hacheck was following the redirects.

We want to fix that, but Nerve considers 3xx to be health check failures.

HAProxy, nginx, Marathon all consider 3xx status codes to be healthy. IMO nerve should be consistent with these other healthcheck consumers (Particularly HAProxy, which nerve is designed to work with).

[Joseph Lynch]

Yea I think it's pretty standard practice to treat 3xxs as healthy. @igor47 @rickypai any objections to #78