Tailor number of delayed_jobs workers on util instances (ExamTime/#6571)

Also introduced a new 'clone' worker that will be responsible for
processing clone jobs.
These are shifted off the web servers to prevent server crashes due to
heavy clone operations.
Merge branch 'issue-6571' of github.com:ExamTime/ey-cloud-recipes into issue-6571

Conflicts:
	cookbooks/delayed_job/recipes/default.rb