INT-3178 Defer Publishing of TCP Open Event

Previously, the TcpConnectionOpenEvent was published as soon
as the socket was connected, but the TcpConnection was not yet
ready for use.

Defer publishing the event until the connection is fully
initialized and registered with the factory and thus available
for use.

Update the test cases to reflect this behavior.

Since the event is now published by the appropriate concrete
factory implementations, enhance the ConnectionToConnectionTests
to verify proper eventing with both Net and NIO implementations.