Use `assetHelper.withCleaner` Within `ApiGwCliBasicTests.scala` Tests

The tests within `incubator-openwhisk-cli/tests/src/test/scala/whisk/core/cli/testApiGwCliBasicTests.scala` tend to not use the `assetHelper` for several action/api tests. Instead, the action and/or api is cleaned up explicitly in each test's `finally` block via `action.delete`. This should be improved to use the `assetHelper` for more concise test code.

The other tests within this repo tend to use this `assetHelper` appropriately, but they all could use a look to make sure the usage is aligned.