The libvirt_storage_backend_sheepdog_priv.la library depends on symbols
provided in the libvirt_driver_storage_impl.la library. As such the
latter must be listed 2nd when passed to the linker to avoid symbol
resolution problems. This mistake is being masked by the sheepdog
driver linking in a second copy of the storage driver code. Remove
this duplicate linkage of backend source and fix the test link order.
Signed-off-by: NDaniel P. Berrangé <berrange@redhat.com>