Allow selection of volume type when creating instance in Horizon

When creating a new instance from an image in the Horizon UI workflow, there is the option to "Create New Volume". The workflow does not allow the user to select the "volume type", and does not default to any of the defined volume types. Allowing the user to select the volume type may be helpful when, for example, the backend allows for different storage options (e.g., performance, thick/thin). These options could be added as metadata to a volume type, and so being able to select the volume type would be useful.