Make WikiPageEntityLookup more robust with attempt to load from DB_MASTER

Try load entity revision from DB_MASTER on failed load from slave.

Fix issue and exception being reported in logs.

Bug: 62547
Change-Id: I440285888f9af5e3d401c974dc5678bd54018832
Merge "Make WikiPageEntityLookup more robust with attempt to load from DB_MASTER"