Snapshots to use preview provider preview display name

[Mark Turner]

Generated snapshots for a test name are numbered:

test_authView_Preview.1.png
test_authView_Preview.2.png
test_authView_Preview.3.png
test_authView_Preview.4.png

Would be better if we supply the preview provider display name so that generated png's have more context:

test_prefireView_Preview.PrefireView.png