Decouple ServiceUpdate to ServerUpdate to be more native (#8138)

The change now is to ensure that we take custom URL as
well for updating the deployment, this is required for
hotfix deliveries for certain deployments - other than
the community release.

This commit changes the previous work d65a2c6725
with newer set of requirements.

Also deprecates PeerUptime()

pkg/madmin/update-commands.go

@@ -0,0 +1,59 @@
+/*
+ * MinIO Cloud Storage, (C) 2019 MinIO, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package madmin
+
+import (
+	"encoding/json"
+	"io/ioutil"
+	"net/http"
+	"net/url"
+)
+
+// ServerUpdateStatus - contains the response of service update API
+type ServerUpdateStatus struct {
+	CurrentVersion string `json:"currentVersion"`
+	UpdatedVersion string `json:"updatedVersion"`
+}
+
+// ServerUpdate - updates and restarts the MinIO cluster to latest version.
+// optionally takes an input URL to specify a custom update binary link
+func (adm *AdminClient) ServerUpdate(updateURL string) (us ServerUpdateStatus, err error) {
+	queryValues := url.Values{}
+	queryValues.Set("updateURL", updateURL)
+
+	// Request API to Restart server
+	resp, err := adm.executeMethod("POST", requestData{
+		relPath:     "/v1/update",
+		queryValues: queryValues,
+	})
+	defer closeResponse(resp)
+	if err != nil {
+		return us, err
+	}
+
+	if resp.StatusCode != http.StatusOK {
+		return us, httpRespToErrorResponse(resp)
+	}
+
+	buf, err := ioutil.ReadAll(resp.Body)
+	if err != nil {
+		return us, err
+	}
+	err = json.Unmarshal(buf, &us)
+	return us, err
+}