KV must not use "asyncio.sleep" directly

[lmazuel]

Instead, should use the sleep from the transport: https://github.com/Azure/azure-sdk-for-python/blob/a53defca65bd47f7fdff0dc14174615b4e7c7007/sdk/core/corehttp/corehttp/runtime/policies/_retry_async.py#L93

You can access the transport from the pipeline context attached to a pipeline request.

Using asyncio prevents usage of trio, and this rule will be enforced in future pylint.