The variable is used for the qemu-specific directory and has a different
meaning of the autoconf "datadir" variable (that's used for the
$prefix/share directory, not for $prefix/share/PACKAGE).

This doesn't change behavior or interfaces, it's just an internal
variable rename.
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>