Backport of Refactor xDS tests into release/1.15.x#16741

hc-github-team-consul-core merged 2 commits intorelease/1.15.xhashicorp/consul:release/1.15.xfrom

backport/add-enterprise-tests/badly-lasting-cardinalhashicorp/consul:backport/add-enterprise-tests/badly-lasting-cardinalCopy head branch name to clipboard