sanity: Uses k8s_test_harness utils

The k8s_test_harness contains commonly used util functions. This
will simplify the tests.

tests/sanity/test_rock.py

@@ -4,7 +4,7 @@
 
 import subprocess
 
-from k8s_test_harness.util import env_util
+from k8s_test_harness.util import docker_util, env_util
 
 
 def _test_sanity(image_version):
@@ -15,12 +15,8 @@ def _test_sanity(image_version):
 
     entrypoint = "/cluster-autoscaler"
     # assert we have the expected files
-    docker_run = subprocess.run(
-        ["docker", "run", "--rm", "--entrypoint", entrypoint, image, "--help"],
-        capture_output=True,
-        text=True,
-    )
-    assert "Usage of /cluster-autoscaler:" in docker_run.stderr
+    process = docker_util.run_in_docker(image, [entrypoint, "--help"])
+    assert "Usage of /cluster-autoscaler:" in process.stderr
 
 
 def test_cluster_autoscaler_1_24_0():