fnctl: fix regression on environment transcription (#232)

Reverts https://github.com/iron-io/functions/pull/225 and prove
correctness with a test.

fnctl/routes.go

@@ -151,7 +151,7 @@ func envAsHeader(req *http.Request, selectedEnv []string) {
 	for _, e := range detectedEnv {
 		kv := strings.Split(e, "=")
 		name := kv[0]
-		req.Header.Set(name, kv[1])
+		req.Header.Set(name, os.Getenv(name))
 	}
 }
 

fnctl/routes_test.go

@@ -0,0 +1,25 @@
+package main
+
+import (
+	"net/http"
+	"os"
+	"testing"
+)
+
+func TestEnvAsHeader(t *testing.T) {
+	const expectedValue = "v=v"
+	os.Setenv("k", expectedValue)
+
+	cases := [][]string{
+		nil,
+		[]string{},
+		[]string{"k"},
+	}
+	for _, selectedEnv := range cases {
+		req, _ := http.NewRequest("GET", "http://www.example.com", nil)
+		envAsHeader(req, selectedEnv)
+		if found := req.Header.Get("k"); found != expectedValue {
+			t.Errorf("not found expected header: %v", found)
+		}
+	}
+}