treat ipv6 addresses correctly

[NixM0nk3y]

When dealing with IPv6 addresses - Sprintf will not do the right thing i.e.

Host: fd00::7c46
Port: 80

Results in upstream target of:

POST /upstreams/myservice.http-svc.80/targets HTTP/1.1
{"target":"fd00::7c46:80","upstream_id":"2e0a4d5a-ed01-4858-ac12-9c3f11df7556"}

Which results in unreachable targets

2018/09/09 14:48:06 [error] 38#38: *22634 connect() failed (113: Host is unreachable) while connecting to upstream, client: fd00::1, server: kong, request: "GET / HTTP/1.1", upstream: "http://[fd00:0000:0000:0000:0000:0000:7c46:0080]:8000/", host: "foo.bar"

The correct API call is:

POST /upstreams/myservice.http-svc.80/targets HTTP/1.1
{"target":"[fd00::7c46]:80","upstream_id":"2e0a4d5a-ed01-4858-ac12-9c3f11df7556"}

golangs standard net.JoinHostPort will do the right thing for both IPv4 + IPv6

[codecov-io]

Codecov Report

Merging #118 into master will not change coverage.
The diff coverage is 0%.

@@           Coverage Diff           @@
##           master     #118   +/-   ##
=======================================
  Coverage   32.09%   32.09%           
=======================================
  Files          33       33           
  Lines        2891     2891           
=======================================
  Hits          928      928           
  Misses       1850     1850           
  Partials      113      113

Impacted Files	Coverage Δ
internal/ingress/controller/kong.go	1.22% <0%> (ø)	⬆️

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[hbagdi]

Verified JoinHostPort() does what it should and Kong processes IPv6 correctly. Will merge shortly.

[hbagdi]

@NixM0nk3y Thank you for taking the time to fix this issue!