Try to list files instead of directory in isolate for gl_cts data. Bug: angleproject:3827 Change-Id: I65ed81886dce185bfc7542c321f43cc9bde6ef92 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1771979 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>