Sets disks in devtest run to sda rather than vda.
Sets disks in devtest run to sda rather than vda.

Fixes issue with mounting ephemeral disk in devtest run with VMs.

Change-Id: I83df0df431760fd87bacd4a2403bff79e9080db7
Closes-Bug: #1294785

rdo-management/tripleo,rdo-management/tripleo