Fix for multithreaded HAProxy (since HAProxy 1.8) (#404)

For making the tcollector work with a multithreaded HAProxy, the pidof command should only get one PID. This is solved with the "-s" (Singleshot).

collectors/0/haproxy.py

@@ -93,7 +93,7 @@
 def haproxy_pid():
   """Finds out the pid of haproxy process"""
   try:
-     pid = subprocess.check_output(["pidof", "haproxy"])
+     pid = subprocess.check_output(["pidof", "-s", "haproxy"])
   except subprocess.CalledProcessError:
      return None
   return pid.rstrip()