TESTS: add a python wrapper for sockpair@

This is a python wrapper which creates a socketpair and passes it as two
environment variable to haproxy.

It's the easiest way to test the sockpair protocol in haproxy.

tests/test-sockpair.py

@@ -0,0 +1,28 @@
+#!/usr/bin/python
+"""
+Python wrapper example to test socketpair protocol
+./test-socketpair.py test.cfg
+
+use sockpair@${FD1} and sockpair@${FD2} in your configuration file
+
+"""
+
+import socket, os, sys
+
+s = socket.socketpair(socket.AF_UNIX, socket.SOCK_STREAM)
+os.set_inheritable(s[0].fileno(), 1)
+os.set_inheritable(s[1].fileno(), 1)
+
+FD1 = s[0].fileno()
+FD2 = s[1].fileno()
+
+print("FD1={} FD2={}".format(FD1, FD2))
+
+os.environ["FD1"] = str(FD1)
+os.environ["FD2"] = str(FD2)
+
+cmd = ["./haproxy",
+       "-f",
+       "{}".format(sys.argv[1])
+]
+os.execve(cmd[0], cmd, os.environ)