tests: treat ECONNRESET as EOF

If the other end of an AF_UNIX stream socket closes the socket without
reading all data, read() and recv() will return ECONNRESET once all data
has been read.  For the purposes of the test suite, this is equivalent
to normal EOF and should be treated as such.

Fixes intermittent failures in test_run_dom0_service_socket_no_read().

qrexec/tests/socket/qrexec.py

@@ -54,7 +54,10 @@ def sendall(self, data):
     def recvall(self, data_len):
         data = b""
         while len(data) < data_len:
-            res = self.conn.recv(data_len - len(data))
+            try:
+                res = self.conn.recv(data_len - len(data))
+            except ConnectionResetError:
+                return data
             if not res:
                 return data
             data += res