Fix hardware_StorageFio test failure

Wrong python code used for testing if file exits.

BUG=chromium:387118
TEST=check locally. Ran hardware_StorageFio on falco.

Change-Id: I2a64dfe9571763694a50eb63d3456b87312c9733
Reviewed-on: https://chromium-review.googlesource.com/204934
Reviewed-by: Puthikorn Voravootivat <puthik@chromium.org>
Reviewed-by: Gwendal Grignou <gwendal@chromium.org>
Commit-Queue: Gwendal Grignou <gwendal@chromium.org>
Tested-by: Gwendal Grignou <gwendal@chromium.org>
1 file changed