[gpu] Exercise new template-generated GPU driver installer

gpu/test_gpu.py:
* using tests from #1275

gpu/verify_pyspark.py:
* new test file ; will probably be moved to mlvm

templates/gpu/install_gpu_driver.sh.in:
* this action template includes only the code unique to this action

gpu/BUILD

@@ -6,7 +6,11 @@ py_test(
     name = "test_gpu",
     size = "enormous",
     srcs = ["test_gpu.py"],
-    data = ["install_gpu_driver.sh", "mig.sh"],
+    data = [
+      "install_gpu_driver.sh",
+      "verify_pyspark.py",
+      "mig.sh"
+    ],
     local = True,
     shard_count = 15,
     deps = [