logging: read all bytes on EOF in event handler

logging: read all bytes on EOF in event handler

If writing side writes enough bytes to the pipe and closes writing
end then we got both VIR_EVENT_HANDLE_HANGUP and VIR_EVENT_HANDLE_READ
in handler. Currently in this situation handler reads 1024 bytes
and finish reading leaving unread data in pipe.

Signed-off-by: Nikolay Shirokovskiy <nshirokovskiy@virtuozzo.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>