Disk Image Import Wizard - `Create new disk image` / `Use existing disk image` names are confusing

Problem/Justification

Yout are not creating a disks image, you are importing one, you are creating a Zvol. This is a needed distinction.

Rename as follows:
-Create new disk image → Create new Zvol
-Use existing disk image → Use existing Zvol

Impact
The current options do not read easily and can be confusing as they do not correctly describe what is happening.

User Story
n/a