Add executable bit to tests directories.

In order for crashes when executables are run from the
/data/local/tests directory, set the executable bit for that
directory and sub-directories. Without this, neither the root
user nor shell user can read any executables or shared libraries in
the tests directory.

Bug: 197229540

Test: Used the crasher executable and copied it to /data/local/tests
Test: and verified that running it as root and shell results in
Test: tombstones that have full unwinds with function names.
Change-Id: Ice669358decad9766e0496c156aa84d4ecacd124