ecore_con/ecore_ipc: flush should wait for connection.

ecore_con/ecore_ipc: flush should wait for connection.

Some applications will create the handle, immediately send data, flush
and delete it, expecting the data to be sent to remote peer.

This is a bad behavior as the application would become unresponsive
until the connection is established, data can be written (since
depends on server consuming it), then allow it to be closed.

A proper behavior here would be to chain based on events, with the
usage of a copier would be simply wait for "done" event.

However the legacy API allowed this and terminology depends on this
awkward "feature", thus be bug-compatible.

This fixes T5015.