Part of work to remove racist language, this name change also improves on the
semantics of this variable name as it was not actually a list of permissible
images but rather a list of images that are required for e2e_node tests that
are to be pre-pulled so that they are available prior to running e2e tests.
Worth noting that this list of images is "union merged" with another list when
setting up e2e_node tests and as such there is the possibilty for overlap.
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