change the vmdk to the one used in VMWare ci

The debian image that defaults to being using with vmware is huge,
and it turns out it's not actually used in VMWare ci so we don't
really know if it's working. Instead use the vmdk that is used
in VMWare ci, which we know will boot, as we get results everyday.

Change-Id: I014746af293852525e2bd128c4d19f5889ecd55d
Merge "change the vmdk to the one used in VMWare ci"
Merge branch 'master' of github.com:openstack-dev/devstack