Clean up and improve test_cel

Improve reliability of attended transfer merge and link tests.
Stop using ast_log(LOG_ERROR, ...); in favor of ast_test_status_update
Remove fred and eve channel helpers since they are not necessary


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@395653 65c4cc65-6c06-0410-ace0-fbb531ad65f3