vdsm.spec: adding {?with_tmpfiles_macro}

The macro %{_tmpfilesdir} was introduced by Fedora 18.
This patch will add a Fedora validation before using it.

Change-Id: I9fb3164fd8c9db7a19379de9975bb05eb60be1db
Signed-off-by: Douglas Schilling Landgraf <dougsland@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/16976
Reviewed-by: Mark Wu <wudxw@linux.vnet.ibm.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>