Refactor bucket delete and bucket policy (#5580)

This commit adds the bucket delete and bucket policy functionalities
to the browser.

Part of rewriting the browser code to follow best practices and
guidelines of React (issues #5409 and #5410)

The backend code has been modified by @krishnasrinivas to prevent
issue #4498 from occuring. The relevant changes have been made to the
code according to the latest commit and the unit tests in the backend.
This commit also addresses issue #5449.

browser/app/js/buckets/__tests__/PolicyInput.test.js

@@ -0,0 +1,77 @@
+/*
+ * Minio Cloud Storage (C) 2018 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.
+ */
+
+import React from "react"
+import { shallow, mount } from "enzyme"
+import { PolicyInput } from "../PolicyInput"
+import { READ_ONLY, WRITE_ONLY, READ_WRITE } from "../../constants"
+import web from "../../web"
+
+jest.mock("../../web", () => ({
+  SetBucketPolicy: jest.fn(() => {
+    return Promise.resolve()
+  })
+}))
+
+describe("PolicyInput", () => {
+  it("should render without crashing", () => {
+    const fetchPolicies = jest.fn()
+    shallow(<PolicyInput currentBucket={"bucket"} fetchPolicies={fetchPolicies}/>)
+  })
+
+  it("should call fetchPolicies after the component has mounted", () => {
+    const fetchPolicies = jest.fn()
+    const wrapper = shallow(
+      <PolicyInput currentBucket={"bucket"} fetchPolicies={fetchPolicies} />
+    )
+    setImmediate(() => {
+      expect(fetchPolicies).toHaveBeenCalled()
+    })
+  })
+
+  it("should call web.setBucketPolicy and fetchPolicies on submit", () => {
+    const fetchPolicies = jest.fn()
+    const wrapper = shallow(
+      <PolicyInput currentBucket={"bucket"} policies={[]} fetchPolicies={fetchPolicies}/>
+    )
+    wrapper.instance().prefix = { value: "baz" }
+    wrapper.instance().policy = { value: READ_ONLY }
+    wrapper.find("button").simulate("click", { preventDefault: jest.fn() })
+
+    expect(web.SetBucketPolicy).toHaveBeenCalledWith({
+      bucketName: "bucket",
+      prefix: "baz",
+      policy: READ_ONLY
+    })
+
+    setImmediate(() => {
+      expect(fetchPolicies).toHaveBeenCalledWith("bucket")
+    })
+  })
+
+  it("should change the prefix '*' to an empty string", () => {
+    const fetchPolicies = jest.fn()
+    const wrapper = shallow(
+      <PolicyInput currentBucket={"bucket"} policies={[]} fetchPolicies={fetchPolicies}/>
+    )
+    wrapper.instance().prefix = { value: "*" }
+    wrapper.instance().policy = { value: READ_ONLY }
+
+    wrapper.find("button").simulate("click", { preventDefault: jest.fn() })
+
+    expect(wrapper.instance().prefix).toEqual({ value: "" })
+  })
+})