RefreshLinksJob performance tweaks.

RefreshLinksJob performance tweaks.

* Made refreshLinksJob2 always spawn smaller jobs. This can reduce
  the problem of all runners doing the same refresh jobs by increasing the
  granularity of the work to single pages parses per job.
* Avoid master queries when fetching the latest revision for refresh links jobs.
  Also avoid the master for template fetching on parse. A LoadBalancer waitFor()
  call is used instead. The main reason for hitting the master to fetch templates
  was this job itself.
* Fixed bug in refreshLinksJob2 where one missing page would cause all the
  remaining updates for pages to be aborted.
* Factored out some code duplication between the two refresh links job classes.

Change-Id: Ieca51567a888f50a6f15b6c2606323da80d6584b