rename role::mediawiki::job_runner -> role::mediawiki::jobrunner

It used to be 'jobrunner', but I renamed it to resolve an ambiguity with
::mediawiki::jobrunner caused by a Puppet parser bug. It can be renamed back
now.

Change-Id: I629781260b62e8719b61ab70b9fcf1fa835146ae
Merge "rename role::mediawiki::job_runner -> role::mediawiki::jobrunner" into production