python: fix chirp broadcasting using '*' interface

• do not send to same broadcast address several times using set instead of list for all bc addresses
• respond to REQUESTs only on the broadcast address the request was received on
• use a timeout on the socket and remove sleep in broadcastmanager
• improve error messages if we run out of file descriptors
• spread out responses by waiting random intervals before responding (Satellites) and scheduling requests better (Controller) Fixes #134 (closed)