be_openssl: get rid off hackish "fd_is_set", to fix some corner cases This patch is a cleanup and a bug fix, it drops ```fd_is_set``` flag, and replace it with some checks to event_initialized(), and now we will not call event_assign() on already added event, plus we will delete event when we really have to (this patch fixes the case when server is down, IOW before this patch we will not call event_del() because ```fd_is_set``` was reset to 0) and this will fix some issues with retries in http layer for ssl. Reported-in: #258 Fixes: regress ssl/bufferevent_socketpair_timeout Fixes: regress ssl/bufferevent_socketpair_timeout_freed_fd