test-patchset: Make a copy of const_structs.checkpatch

Currently aiaiai issues the following warning for each patch under test
because recent versions of checkpatch look for a list of structures in
scripts/const_structs.checkpatch .

This patch fixes the problem by copying out the extra file (if one is
found).

Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>