baremetal: Remove depenency on libvirt's fetch_image method

It's messy for virt-drivers to depend on each other, so this patch alters
baremetal to use the cross-driver fetch function, instead of the libvirt
version.

Change-Id: I910c621452fa7eb9add417a8738e5757aeb1a48c
Merge "baremetal: Remove depenency on libvirt's fetch_image method"