adapt `foreachwiki` for labs

The foreachwiki script was always attempting to use all.dblist which the
list of production wiki.  On beta labs, we use the all-labs.dblist.

bug: 41285
Change-Id: Ib0f0f1851e3f131b34d6cc7e392112059ef36ae7
Merge "adapt `foreachwiki` for labs" into production