thick-plugin: refactor multus

Multus is refactored as a thick plugin, featuring 2 main components:
  - a server listening to a unix domain socket, running in a pod
  - a shim, a binary on the host that will send JSON requests built from
    its environment / stdin values to the aforementioned server.

The pod where the multus daemon is running must share the host's PID
namespace.

Signed-off-by: Miguel Duarte Barroso <mdbarroso@redhat.com>

react to maintainers review

Signed-off-by: Miguel Duarte Barroso <mdbarroso@redhat.com>

thick, deployment: update the daemonset spec

Signed-off-by: Miguel Duarte Barroso <mdbarroso@redhat.com>

thick, config: validate the cni config passed by the runtime

Without this patch, we're blindly trusting anything sent by the server.
This way, we assure the requests arriving at the multus controller are
valid before hand.

Signed-off-by: Miguel Duarte Barroso <mdbarroso@redhat.com>

thick: model client / server config

Also add a new command line parameter on the multus controller, pointing
it to the server configuration.

Signed-off-by: Miguel Duarte Barroso <mdbarroso@redhat.com>

SQUASH candidate, thick, config: cleanup the configuration

Signed-off-by: Miguel Duarte Barroso <mdbarroso@redhat.com>

multus: use args.args instead of an env variable

CNI is already filling the args structure; we should consume that
rather than rely on the environment variables.

Signed-off-by: Miguel Duarte Barroso <mdbarroso@redhat.com>

unit tests: remove weird tests that check an impossible scenario

Signed-off-by: Miguel Duarte Barroso <mdbarroso@redhat.com>

docs, thick: document the thick plugin variant

Signed-off-by: Miguel Duarte Barroso <mdbarroso@redhat.com>

thick, server, multus: re-use common types

Signed-off-by: Miguel Duarte Barroso <mdbarroso@redhat.com>

vendor/github.com/gorilla/mux/test_helpers.go

@@ -0,0 +1,19 @@
+// Copyright 2012 The Gorilla Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package mux
+
+import "net/http"
+
+// SetURLVars sets the URL variables for the given request, to be accessed via
+// mux.Vars for testing route behaviour. Arguments are not modified, a shallow
+// copy is returned.
+//
+// This API should only be used for testing purposes; it provides a way to
+// inject variables into the request context. Alternatively, URL variables
+// can be set by making a route that captures the required variables,
+// starting a server and sending the request to that server.
+func SetURLVars(r *http.Request, val map[string]string) *http.Request {
+	return requestWithVars(r, val)
+}