Glance V1 API is deprecated and the V2 API is CURRENT now.
So this patch changess the default value of used Glance API to use
the V2 API.
NOTE: Nova team also has removed the config option for using Glance
V1 API since Id891172418535a88fefb8ea05d774fe39dc14eaf .
Change-Id: I54db379f6fbe859fd9f1b0cdd5b74102539ab265