errorlib: hostname in error notifications
errorlib: hostname in error notifications

* Adds hostname to subject line of emergency notification
  e-mails. (closes #1546)

Reviewed-by: Jan Aage Lavik <8d55e006a1b29770f275a5c59a7341f17f8e69d5@cern.ch>

tiborsimko/invenio,inveniosoftware/invenio,tiborsimko/invenio,inveniosoftware/invenio