Send mail if job offer form is flooded

Mail is sent only when flood is detected, but not for following
submission failures.
4 jobs for develop in 55 seconds (queued for 1 second)
Status Name Job ID Coverage
  Deps
passed deps #19961
pelican

00:00:02

 
  Build
passed build #19962
docker

00:00:28

 
  Deploy
passed apache-dev #19963
pelican

00:00:10

 
  Post Deploy
passed update-issue #19964
docker

00:00:14