update IoT Device Update to use azure_svc_deviceupdate

[cataggar]

IoT Device Update is a recent contribution in #694 by @rerkcp. @bmc-msft made some modifications in #716, but is also looking at updating it to build on top of the azure_svc_deviceupdate generated crate. In general, this is the pattern we wish to support. This will be the first sdk here to do so.

This crate has not yet been published. I think we rename it to azure_iot_deviceupdate following the naming conventions. NuGet is similar: https://www.nuget.org/packages/Azure.IoT.DeviceUpdate. The folder should also be git mv to iot_deviceupdate.