Socket tests for each loop implementation

[igorw]

[steverhoades]

I think I can help with this one as I just finished implementing this for LibUvLoopTest. Honestly, I think we should strongly consider making all EventLoops only accept network related sockets - i've done that in LIbUvLoop for now as otherwise libuv SIGABRTs.

[clue]

See reactphp/event-loop#66