Support content-type negotiation in the API server

A NegotiatedSerializer is passed into the API installer (and
ParameterCodec, which abstracts conversion of query params) that can be
used to negotiate client/server request/response serialization. All
error paths are now negotiation aware, and are at least minimally
version aware.

Watch is specially coded to only allow application/json - a follow up
change will convert it to use negotiation.

Ensure the swagger scheme will include supported serializations - this
now includes application/yaml as a negotiated option.

test/integration/master_test.go

@@ -51,3 +51,73 @@ func TestWatchSucceedsWithoutArgs(t *testing.T) {
 	}
 	resp.Body.Close()
 }
+
+func TestAccept(t *testing.T) {
+	_, s := framework.RunAMaster(t)
+	defer s.Close()
+
+	resp, err := http.Get(s.URL + "/api/")
+	if err != nil {
+		t.Fatalf("unexpected error getting api: %v", err)
+	}
+	if resp.StatusCode != http.StatusOK {
+		t.Fatalf("got status %v instead of 200 OK", resp.StatusCode)
+	}
+
+	body, _ := ioutil.ReadAll(resp.Body)
+	if resp.Header.Get("Content-Type") != "application/json" {
+		t.Errorf("unexpected content: %s", body)
+	}
+	if err := json.Unmarshal(body, &map[string]interface{}{}); err != nil {
+		t.Fatal(err)
+	}
+
+	req, err := http.NewRequest("GET", s.URL+"/api/", nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	req.Header.Set("Accept", "application/yaml")
+	resp, err = http.DefaultClient.Do(req)
+	if err != nil {
+		t.Fatal(err)
+	}
+	body, _ = ioutil.ReadAll(resp.Body)
+	if resp.Header.Get("Content-Type") != "application/yaml" {
+		t.Errorf("unexpected content: %s", body)
+	}
+	t.Logf("body: %s", body)
+	if err := yaml.Unmarshal(body, &map[string]interface{}{}); err != nil {
+		t.Fatal(err)
+	}
+
+	req, err = http.NewRequest("GET", s.URL+"/api/", nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	req.Header.Set("Accept", "application/json, application/yaml")
+	resp, err = http.DefaultClient.Do(req)
+	if err != nil {
+		t.Fatal(err)
+	}
+	body, _ = ioutil.ReadAll(resp.Body)
+	if resp.Header.Get("Content-Type") != "application/json" {
+		t.Errorf("unexpected content: %s", body)
+	}
+	t.Logf("body: %s", body)
+	if err := yaml.Unmarshal(body, &map[string]interface{}{}); err != nil {
+		t.Fatal(err)
+	}
+
+	req, err = http.NewRequest("GET", s.URL+"/api/", nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	req.Header.Set("Accept", "application") // not a valid media type
+	resp, err = http.DefaultClient.Do(req)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if resp.StatusCode != http.StatusNotAcceptable {
+		t.Errorf("unexpected error from the server")
+	}
+}