=act #3602 report `Connected` only when connection attempt was successful

Before this change, a client connection was always instantly reported as
`Connected`, even if the endpoint would never respond at all.

The reason is a weird behavior of OP_CONNECT and SocketChannel in the
JDK (observed in Linux):
 - a channel is always connectable before the connection is attempted
   (`channel.connect`). Selecting for OP_CONNECT before the `connect`
   call will instantly report connectable
 - even worse: after OP_CONNECT was reported true, also `finishConnect`
   will always return true, even if the connection wasn't yet established.
   That's probably the case because `finishConnect` is internally implemented
   depending on previous epoll results (on Linux).
Merge pull request #1729 from jrudolph/wip-3602-fix-connected

=act #3602 report `Connected` only when connection attempt was successful