mediawiki: Redo cURL dispatcher config for jobrunner

* Move jobrunner.conf.erb to templates/jobrunner
* Choose dispatcher command by selecting a template name based on the distro
  release name (precise/trusty).

This reverts commit 3f2beeb4b10fb2156edb0f2c3550c1321815c5aa.

Change-Id: I725eecc93ae866c59d85e203126e37e73cc91ae8