Add a mechanism for python test server to exit

This CL adds a mechanism which can be used to make the python test server exit.

BUG=417684

Review URL: https://codereview.chromium.org/607823002

Cr-Commit-Position: refs/heads/master@{#296920}

chrome/browser/policy/test/policy_testserver.py

@@ -229,6 +229,13 @@ class PolicyRequestHandler(BaseHTTPServer.BaseHTTPRequestHandler):
     path = self.path if sep == -1 else self.path[:sep]
     if path == '/externalpolicydata':
       http_response, raw_reply = self.HandleExternalPolicyDataRequest()
+    elif path == '/configuration/test/exit':
+      # This is not part of the standard DM server protocol.
+      # This extension is added to make the test server exit gracefully
+      # when the test is complete.
+      self.server.stop = True
+      http_response = 200
+      raw_reply = 'OK'
     else:
       http_response = 404
       raw_reply = 'Invalid path'