I think I may have figured this out.  I had been bumping into the same problem (stalling at the P2P connection) on some coins but not others.  I finally realized I was wrong in an initial assumption...the P2P_PREFIX setting in bitcoin/networks.py is in fact a coin-specific setting -- which is logical, as the other settings in that file are coin-specific as well.   In fact, it looks like it is basically the "magic value" or "magic number" referred to in https://en.bitcoin.it/wiki/Protocol_specification, and after poking around in the code I think you can find it in main.cpp at pchMessageStart[4]=...  Using this specific value as the P2P_PREFIX fixed the problem for me.

So, for example, I haven't ever installed Dragoncoin myself, but looking quickly at the relevant line in main.cpp:


Thus, for Dragoncoin, try setting


and let us know if that gets you past stalling at the P2P connection.

Hope this is helpful.