ephemeral-device config pluralization is misleading

[Adam Dyess]

  ephemeral-device:
    description: |
      Block devices to use for storage of ephermeral disks to support nova
      instances; generally used in-conjunction with 'encrypt' to support
      data-at-rest encryption of instance direct attached storage volumes.
    source: user
    type: string
    value: /dev/disk/by-dname/bcache-ephemeral

The plural words "devices" and "disks" imply this config supports MULTIPLE block devices. It would be REALLY nice if the charm did support multiple block devices via a comma separated list

/dev/disk/by-dname/bcache-ephemeral,/dev/disk/by-dname/ssd-os-part4

the first block device in the list can be chosen as the block device for ephemerals

[Adam Dyess (addyess)]

When two metals have different block devices that cannot be mapped to the same /dev/disk/..., it looks like the charm will allow you to do this

juju config nova-compute ephemeral-device=/path/number/1
juju add-unit nova-compute --to <machines-with /path/number/1 but NOT /path/number/2>
...wait...
juju config nova-compute ephemeral-device=/path/number/2
juju add-unit nova-compute --to <machines-with /path/number/2 but NOT /path/number/1>
...wait more...

It seems the code would set up both correctly. Is this a dangerous workaround?