Refactor faasd and faas-containerd merge

The use of containerd and CNI functions has been refactored to reuse
the same codebase.

Added all network functionality to own directory and package. Removed
netlink and weave library in favor of using CNI plugin result files.

Rename containers handler to functions to clear-up functionality.

Signed-off-by: Carlos de Paula <me@carlosedp.com>

pkg/cninetwork/netns.go

@@ -0,0 +1,66 @@
+// +build go1.10
+
+// Copyright Weaveworks
+// github.com/weaveworks/weave/net
+
+package cninetwork
+
+import (
+	"errors"
+	"fmt"
+	"path/filepath"
+	"runtime"
+
+	"github.com/vishvananda/netlink"
+	"github.com/vishvananda/netns"
+)
+
+var ErrLinkNotFound = errors.New("Link not found")
+
+func WithNetNS(ns netns.NsHandle, work func() error) error {
+	runtime.LockOSThread()
+	defer runtime.UnlockOSThread()
+
+	oldNs, err := netns.Get()
+	if err == nil {
+		defer oldNs.Close()
+
+		err = netns.Set(ns)
+		if err == nil {
+			defer netns.Set(oldNs)
+
+			err = work()
+		}
+	}
+
+	return err
+}
+
+func WithNetNSLink(ns netns.NsHandle, ifName string, work func(link netlink.Link) error) error {
+	return WithNetNS(ns, func() error {
+		link, err := netlink.LinkByName(ifName)
+		if err != nil {
+			if err.Error() == errors.New("Link not found").Error() {
+				return ErrLinkNotFound
+			}
+			return err
+		}
+		return work(link)
+	})
+}
+
+func WithNetNSByPath(path string, work func() error) error {
+	ns, err := netns.GetFromPath(path)
+	if err != nil {
+		return err
+	}
+	return WithNetNS(ns, work)
+}
+
+func NSPathByPid(pid int) string {
+	return NSPathByPidWithRoot("/", pid)
+}
+
+func NSPathByPidWithRoot(root string, pid int) string {
+	return filepath.Join(root, fmt.Sprintf("/proc/%d/ns/net", pid))
+}