Have letsencrypt-auto do a real upgrade in leauto-upgrades option 2 (#5390)

* Make leauto_upgrades do a real upgrade

* Cleanup vars and output

* Sleep until the server is ready

* add simple_http_server.py

* Use a randomly assigned port

* s/realpath/readlink

* wait for server before getting port

* s/localhost/all interfaces

tools/simple_http_server.py

@@ -0,0 +1,26 @@
+#!/usr/bin/env python
+"""A version of Python 2.x's SimpleHTTPServer that flushes its output."""
+from BaseHTTPServer import HTTPServer
+from SimpleHTTPServer import SimpleHTTPRequestHandler
+import sys
+
+def serve_forever(port=0):
+    """Spins up an HTTP server on all interfaces and the given port.
+
+    A message is printed to stdout specifying the address and port being used
+    by the server.
+
+    :param int port: port number to use.
+
+    """
+    server = HTTPServer(('', port), SimpleHTTPRequestHandler)
+    print 'Serving HTTP on {0} port {1} ...'.format(*server.server_address)
+    sys.stdout.flush()
+    server.serve_forever()
+
+
+if __name__ == '__main__':
+    kwargs = {}
+    if len(sys.argv) > 1:
+        kwargs['port'] = int(sys.argv[1])
+    serve_forever(**kwargs)