Add initial containerd *Client

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

client_test.go

@@ -0,0 +1,18 @@
+package containerd
+
+import "testing"
+
+const defaultAddress = "/run/containerd/containerd.sock"
+
+func TestNewClient(t *testing.T) {
+	client, err := New(defaultAddress)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if client == nil {
+		t.Fatal("New() returned nil client")
+	}
+	if err := client.Close(); err != nil {
+		t.Errorf("client closed returned errror %v", err)
+	}
+}