handle SkuNotAvailable errors when creating VM Scalesets

[bmc-msft]

Example exception that is now handled:

Exception while executing function: Functions.timer_workers 
Result: Failure
Exception: ResourceExistsError: (SkuNotAvailable) The requested size for resource '/subscriptions/GUID/resourceGroups/RESOURCE_GROUP_NAME/providers/Microsoft.Compute/virtualMachineScaleSets/GUID' is currently not available in location 'REGION' zones '' for subscription 'GUID'. Please try another size or deploy to a different location or zones. See https://aka.ms/azureskunotavailable for details.

NOTE: This change uses the repr of the exception to remove the complexity of searching through nested ODataV4Format errors that make up the exception record.

[bmc-msft]

NOTE: On a subscription where the VM quotas are maxed out, the integration tests fail appropriately with the following error:

ERROR:integration:task scaleset failed: linux-trivial-crash-afl - generic_crash_report - creation_failed (code=<ErrorCode.VM_CREATE_FAILED: 461> errors=["creating vmss: (SkuNotAvailable) The requested size for resource '/subscriptions/GUID/resourceGroups/GROUP/providers/Microsoft.Compute/virtualMachineScaleSets/GUID' is currently not available in location 'REGION' zones '' for subscription 'GUID'. Please try another size or deploy to a different location or zones. See https://aka.ms/azureskunotavailable for details."])