Add mysterious table to the union

Suddenly most of the performance data moved to a new table
called MultimediaViewerNetworkPerformance_7917896_1

We need to query it as well, otherwise we're not getting any
recent data

Change-Id: I0559744c61b2a0f0a114f2ded5992918b0308628
Mingle: https://wikimedia.mingle.thoughtworks.com/projects/multimedia/cards/596