provider/azure: try to fetch userdata from IMDS
provider/azure: try to fetch userdata from IMDS

Azure userdata fetching is now divided into two parts:
* try to fetch userdata from IMDS
* in case of failure: try to fetch custom data from CDROM

Signed-off-by: Mathieu Tortuyaux <209226b75cd10daab93d895d8cef16970a1da9ee@microsoft.com>

coreos/ignition,coreos/ignition,coreos/ignition