Azure: cloud-init skips formatting the resource disk (ephemeral0) when there is additional data disks' configuration in user-data

This bug was originally filed in Launchpad as [LP: #1879552](https://bugs.launchpad.net/cloud-init/+bug/1879552)

Launchpad details

affected_projects = []

assignee = None

assignee_name = None

date_closed = None

date_created = 2020-05-19T19:14:22.237422+00:00

date_fix_committed = None

date_fix_released = None

id = 1879552

importance = undecided

is_complete = False

lp_url = https://bugs.launchpad.net/cloud-init/+bug/1879552

milestone = None

owner = vtqanh

owner_name = Anh Vo (MSFT)

private = False

status = confirmed

submitter = vtqanh

submitter_name = Anh Vo (MSFT)

tags = ['azure']

duplicates = []

_Launchpad user **Anh Vo (MSFT)(vtqanh)** wrote on 2020-05-19T19:14:22.237422+00:00_

Deploying a bionic VM on Azure (Canonical:UbuntunServer:18.04-LTS:latest) with VM Size Standard_DS1_V2 and an additional datadisk with the following config

#cloud-config

disk_setup:
/dev/disk/azure/scsi1/lun0:
table_type: gpt
layout: True
overwrite: True

fs_setup:
- device: /dev/disk/azure/scsi1/lun0
partition: 1
filesystem: ext4

mounts:
- [ /dev/disk/azure/scsi1/lun0, /datadisk1, "ext4", "defaults,nofail,discard", "0", "0" ]

Expected Result:
+ Resource disk (ephemeral0) is formatted as ext4 and mounted to /mnt (which is what happens without attaching the data disk)

Actual Result:
+ Resource disk is partitioned but not formatted, got mounted to /mnt as ntfs

I used this command to create a VM with datadisk and passing in custom data
az vm create -g -n vmname --image Canonical:UbuntuServer:18.04-LTS:latest --admin-username adminuser --ssh-key-value @/home/user/.ssh/key.pub --boot-diagnostics-storage storage_account --size Standard_DS1_V2 --custom-data ./customdata.yml --data-disk-sizes-gb 32

I have attached the cloud-init log and the custom data