Initial merge of faas-containerd

This patch completes part of the work in #20 by porting the code
for faas-containerd in-tree. When tested, I was able to deploy
and then remove figlet from the store on `x86_64`.

In a follow-up PR, duplication will be removed where possible
and consolidated with updated documentation.

Signed-off-by: Alex Ellis (OpenFaaS Ltd) <alexellis2@gmail.com>

pkg/provider/handlers/invoke_resolver.go

@@ -0,0 +1,39 @@
+package handlers
+
+import (
+	"fmt"
+	"log"
+	"net/url"
+
+	"github.com/containerd/containerd"
+)
+
+const watchdogPort = 8080
+
+type InvokeResolver struct {
+	client *containerd.Client
+}
+
+func NewInvokeResolver(client *containerd.Client) *InvokeResolver {
+	return &InvokeResolver{client: client}
+}
+
+func (i *InvokeResolver) Resolve(functionName string) (url.URL, error) {
+	log.Printf("Resolve: %q\n", functionName)
+
+	function, err := GetFunction(i.client, functionName)
+	if err != nil {
+		return url.URL{}, fmt.Errorf("%s not found", functionName)
+	}
+
+	serviceIP := function.IP
+
+	urlStr := fmt.Sprintf("http://%s:%d", serviceIP, watchdogPort)
+
+	urlRes, err := url.Parse(urlStr)
+	if err != nil {
+		return url.URL{}, err
+	}
+
+	return *urlRes, nil
+}