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: http://svn.asterisk.org/svn/asterisk/trunk@395653 f38db490-d61c-443f-a65b-d21fe96a405b