cleanup: go vet and golint run (#736)

* cleanup: go vet and golint run

Various cleanups trickered by go vet and golint.

* Fix tests and lowercase all errors

Lowercase all errors, some tests in kubernetes use errors from
kubernetes which do start with a capital letter.

middleware/proxy/dns.go

@@ -15,6 +15,7 @@ type dnsEx struct {
 	Options
 }
 
+// Options define the options understood by dns.Exchange.
 type Options struct {
 	ForceTCP bool // If true use TCP for upstream no matter what
 }

middleware/proxy/lookup.go

@@ -17,7 +17,7 @@ func NewLookup(hosts []string) Proxy {
 	return NewLookupWithOption(hosts, Options{})
 }
 
-// NewLookupWithForcedProto process creates a simple round robin forward with potentially forced proto for upstream.
+// NewLookupWithOption process creates a simple round robin forward with potentially forced proto for upstream.
 func NewLookupWithOption(hosts []string, opts Options) Proxy {
 	p := Proxy{Next: nil}