provider/openstack: Multi Ephemeral Disk Support

[jtopjian]

This commit adds the ability to create instances with multiple ephemeral (local) disks.

Fixes #4042
Fixes #5098

[afritzler]

@jtopjian I tested the RP on our OpenStack and it is looking good. I managed to split up a 4TB ephemeral disk into 4 single block devices.

One note though regarding the boot device:

    block_device {
      boot_index = 0
      delete_on_termination = true
      destination_type = "local"
      source_type = "image"
      uuid = "<image uuid>"
    }

Did I get it correct, that the block device (index=0) is mandatory? Because I could not create an instance without it. Also, it would be great to use the image_name instead of the uuid.

[jtopjian]

@afritzler Yes, I think boot_index = 0 is required. Good point about image_name instead of uuid. I think I'll work in getting this PR merged and then work on image_name as an enhancement.

[afritzler]

Btw. one more thing regarding guest_format = "ext4": is this flag actually doing something? I ended up with an unformatted vanilla disk.

[jtopjian]

@afritzler To be honest, I'm not sure. I'd have to dig into the actual Nova API code to look. However, guest_format is being passed to the Nova API when nova boot is run on the command line (Check the nodes from #4042), so it might be a good idea to include it from the very start.

Edit: never mind, it's an optional attribute. You can safely omit it. Documentation has been updated. :)

[ghost]

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