XXX testing/utils: Make ManagedHTTPServer threaded

It's used in context where many clients can connect in the same exact time,
like HAProxy balancer and real clients, which can result with seeing this
server as down.

XXX:
 * maybe it shall be selectable depending on the testing context...

slapos/testing/utils.py

@@ -40,6 +40,7 @@ import json
 from contextlib import closing
 from six.moves import BaseHTTPServer
 from six.moves import urllib_parse
+from http.server import HTTPServer
 
 from ..grid.utils import getPythonExecutableFromSoftwarePath
 
@@ -142,7 +143,7 @@ class ManagedHTTPServer(ManagedResource):
     """
     logger = self._cls.logger
 
-    class ErrorLoggingHTTPServer(BaseHTTPServer.HTTPServer):
+    class ErrorLoggingThreadedHTTPServer(ThreadingMixIn, BaseHTTPServer.HTTPServer):
       def handle_error(self, request , client_addr):
         # redirect errors to log
         logger.info("Error processing request from %s", client_addr, exc_info=True)
@@ -154,7 +155,7 @@ class ManagedHTTPServer(ManagedResource):
         self.hostname,
         self.port,
     )
-    server = ErrorLoggingHTTPServer(
+    server = ErrorLoggingThreadedHTTPServer(
         (self.hostname, self.port),
         self.RequestHandler,
     )