Cluster: clusterProcessPacket() was not 80 cols friendly.

The function actually needs to be split into sub-functions at some
point in the future.
anetTcpGenericConnect() code improved + 1 bug fix.

Now the socket is closed if anetNonBlock() fails, and in general the
code structure makes it harder to introduce this kind of bugs in the
future.

Reference: pull request #1059.
Remove useless goto from anetTcpGenericConnect().
anetTcpGenericConnect() bug introduced in 9d19977 fixed.

Durign a refactoring I mispelled _port for port.
This is one of the reasons I never used _varname myself.
anetPeerToString / SockName: port can be NULL on errors too.
Log disconnection with slave only when ip:port is available.