This is needed specifically by XTS, but it might be useful for other
external suites that want to move files out of their runtime directories
into the saved directory. Specifically if those files are linked into
the summary.

v3: - Add the results_dir name definition to the constructor

Signed-off-by: Dylan Baker <baker.dylan.c@gmail.com>
Reviewed-by: Eric Anholt <eric@anholt.net> (v2)