Fetch volume_types by uuid and not by name in v2

This was left over from the UUID switch. Looking up volume_types by name
is deprecated in v1 and removed in v2.

Fixes: bug #1087817
Change-Id: I02cc035565f9496cd5af228c55ced5cafef2ad81
Merge "Fetch volume_types by uuid and not by name in v2"