cast Path to string type

os.path.isdir, os.path.exists cannot handle Path type until python 3.5
so cat Path to string type

Bug: 138639389
Test: development/vndk/tools/image-diff-tool/compare_images_and_print.sh "-t path1 path2 -s SYSTEM -i"
Change-Id: I147eac6f2548558737409a7a93ac54f0053a072e
1 file changed