Switch to more efficient and compact test setup.

tests/README.md

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+# Ansible Role tests
+
+To run the test playbook(s) in this directory:
+
+  1. Install and start Docker.
+  1. Download the test shim (see .travis.yml file for the URL) into `tests/test.sh`:
+    - `wget -O tests/test.sh wget -O ${PWD}/tests/test.sh https://gist.githubusercontent.com/geerlingguy/73ef1e5ee45d8694570f334be385e181/raw/`
+  1. Make the test shim executable: `chmod +x tests/test.sh`.
+  1. Run (from the role root directory) `distro=[distro] playbook=[playbook] ./tests/test.sh`
+
+If you don't want the container to be automatically deleted after the test playbook is run, add the following environment variables: `cleanup=false container_id=$(date +%s)`