Adds Done() and Err() to pod controller (#735)

Allows callers to wait for pod controller exit in addition to readiness.
This means the caller does not have to deal handling errors from the pod
controller running in a gorutine since it can wait for exit via `Done()`
and check the error with `Err()`

node/podcontroller_test.go

@@ -0,0 +1,44 @@
+package node
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"gotest.tools/assert"
+)
+
+func TestPodControllerExitOnContextCancel(t *testing.T) {
+	tc := newTestController()
+	ctx := context.Background()
+	ctxRun, cancel := context.WithCancel(ctx)
+
+	done := make(chan error)
+	go func() {
+		done <- tc.Run(ctxRun, 1)
+	}()
+
+	ctxT, cancelT := context.WithTimeout(ctx, 30*time.Second)
+	select {
+	case <-ctx.Done():
+		assert.NilError(t, ctxT.Err())
+	case <-tc.Ready():
+	case <-tc.Done():
+	}
+	assert.NilError(t, tc.Err())
+
+	cancelT()
+
+	cancel()
+
+	ctxT, cancelT = context.WithTimeout(ctx, 30*time.Second)
+	defer cancelT()
+
+	select {
+	case <-ctxT.Done():
+		assert.NilError(t, ctxT.Err(), "timeout waiting for Run() to exit")
+	case err := <-done:
+		assert.NilError(t, err)
+	}
+	assert.NilError(t, tc.Err())
+}