Implement part of #27617 [expend checksum format to <algorithm>:(<checksum>|<url>)] (#43751)

* expend checksum format to <algorithm>:(<checksum>|<url>)

* continue to code at office

* ALPHA - expend checksum format to <algorithm>:(<checksum>|<url>)

* clean up tmpfile and comment

* try to add test code for 27617

* try to add test code for 27617

* try to add test code for 27617

* try to fix [Could not find or access 'testserver.py']

* fix test code [Could not find or access 'testserver.py']

* fix test code [add files dir]

* fix test code [files dir not exists]

* as [connection was closed before a valid response was received]

* [connection was closed before a valid response was received]

* [connection was closed before a valid response was received]

* add test item [sha1 and sha256]

* since [connection was closed before a valid response was received]

* fix [connection was closed before a valid response was received]

* fix test code typo

* add docs for #27617

* PR #43751 is minor change

* fix pep8 issue.

* fix test code style.

* fix unexpected quote

test/integration/targets/get_url/files/testserver.py

@@ -0,0 +1,20 @@
+import sys
+
+if __name__ == '__main__':
+    if sys.version_info[0] >= 3:
+        import http.server
+        import socketserver
+        PORT = int(sys.argv[1])
+
+        class Handler(http.server.SimpleHTTPRequestHandler):
+            pass
+
+        Handler.extensions_map['.json'] = 'application/json'
+        httpd = socketserver.TCPServer(("", PORT), Handler)
+        httpd.serve_forever()
+    else:
+        import mimetypes
+        mimetypes.init()
+        mimetypes.add_type('application/json', '.json')
+        import SimpleHTTPServer
+        SimpleHTTPServer.test()