test utils: replace literal slice declarations with nil slices
test utils: replace literal slice declarations with nil slices

See https://github.com/golang/go/wiki/CodeReviewComments#declaring-empty-slices

Signed-off-by: Jed Lejosne <58df768959dd06ee96a0a2c42d6cb59ebc2cc6b8@redhat.com>

kubevirt/kubevirt,kubevirt/kubevirt,kubevirt/kubevirt,kubevirt/kubevirt