Split testImageusage into four tests

There is a reoccurring problem with this test method on English Wikipedia.
As the test currently has four different sets of tests, it is not 100%
reliable to determine which queries are causing the problem.

Output message regarding which image is being used in these tests.

Bug: 71971
Change-Id: I8443bc0f55ff77b8fc266f55c2bfbf32940be892
Merge "Split testImageusage into four tests"