Apply the 'ssl-redirect' annotation per-location

[ankon]

This is needed to avoid ingress definitions with different settings for SSL
redirection conflicting with each other.

NB: This was discussed in the review of #427, but ultimately not addressed.

---

In my test setup I have regular ingress definitions with enabled SSL-redirect, and kube-lego is adding '/.well-known/acme-challenge/...' ingress definitions that at least for a while need to not use ssl-redirection. In kube-lego's log files one can see the problem:

time="2017-06-27T10:29:01Z" level=debug msg="testing reachability of http://DOMAIN.TLD/.well-known/acme-challenge/_selftest" context=acme domain=DOMAIN.TLD
time="2017-06-27T10:29:01Z" level=debug msg="error while authorizing: reachability test failed: Get https://DOMAIN.TLD/.well-known/acme-challenge/_selftest: x509: certificate signed by unknown authority" context=acme domain=DOMAIN.TLD

Note that the reachability test wants to use 'http' (see https://github.com/jetstack/kube-lego/blob/master/pkg/acme/cert_request.go#L47 for the request, and https://github.com/jetstack/kube-lego/blob/master/pkg/provider/nginx/nginx.go#L119 for the ingress configuration using ssl-redirect=false), but then follows the redirect to 'https' -- which uses the "Kubernetes Ingress Controller Fake Certificate".

[k8s-reviewable]

This change is 

[coveralls]

Coverage increased (+0.01%) to 44.329% when pulling 04346a8 on Collaborne:pr/redirect-per-location into 005ed52 on kubernetes:master.

[aledbf]

/lgtm

[aledbf]

@ankon thanks!