Make add_test_data destination path explicit
Make add_test_data destination path explicit

When adding subdirectories there was opptunitiy for the wrong thing
to happen due to diffrences between how paths with and without trailing
slashes are handled by cp. For example consider:

/tmp/latest-test-data/
  (Empty)
test/data/ui-screenshots/
  foo.png

Then this command:
cp -r test/data/ui-screenshots /tmp/latest-test-data/

Produces the desired output:
/tmp/latest-test-data/
  ui-screenshots/
    foo.png

However the command:
cp -r test/data/ui-screenshots/ /tmp/latest-test-data/

(Note the trailing /) produces incorrect output:
/tmp/latest-test-data/
  foo.png

We can avoid this by being explicit about the output directory:
cp -r test/data/ui-screenshots /tmp/latest-test-data/ui-screenshots
cp -r test/data/ui-screenshots/ /tmp/latest-test-data/ui-screenshots/

In which case both forms to work (assuming ui-screenshots does not exist
which it will not since we delete it on the previous line).

Change-Id: Icd39a1dcea99dec17c3cf14d1640b881e22edacc

google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto