Add initial containerd *Client

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

container_test.go

@@ -0,0 +1,23 @@
+package containerd
+
+import (
+	"context"
+	"testing"
+)
+
+func TestContainerList(t *testing.T) {
+	client, err := New(defaultAddress)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer client.Close()
+
+	containers, err := client.Containers(context.Background())
+	if err != nil {
+		t.Errorf("container list returned error %v", err)
+		return
+	}
+	if len(containers) != 0 {
+		t.Errorf("expected 0 containers but received %d", len(containers))
+	}
+}