testing: fix resource warning with ManagedHTTPServer

We fork a subprocess to serve requests, but the listening socket is bound
in server constructor and inherited by subprocess. With this pattern, we
have to explicitly close the socket from parent process to prevent the
leak.

slapos/testing/testcase.py

@@ -320,7 +320,7 @@ class SlapOSInstanceTestCase(unittest.TestCase):
     # type: (str, Type[ManagedResourceType]) -> ManagedResourceType
     """Get the managed resource for this name.
 
-    If resouce was not created yet, it is created and `open`. The
+    If resource was not created yet, it is created and `open`. The
     resource will automatically be `close` at the end of the test
     class.
     """

slapos/testing/utils.py

@@ -172,6 +172,8 @@ class ManagedHTTPServer(ManagedResource):
         name=self._name,
     )
     self._process.start()
+    # from now on, socket is used by server subprocess, we can close it
+    server.socket.close()
 
   def close(self):
     # type: () -> None