celery: email address for errors
celery: email address for errors

* Changes default Celery email address for errors to always be
  CFG_SITE_ADMIN_EMAIL.

Signed-off-by: Lars Holm Nielsen <7eaffca9f7cd98839b5821d0d23e09ff764b82cd@cern.ch>

tiborsimko/invenio-celery,inveniosoftware/invenio-celery,tiborsimko/invenio-celery,inveniosoftware/invenio-celery