Allow MLTS/build_and_run_benchmark.sh to work on release images.

- Exported utility activities
- Created TestExternalStorageActivity as a helper for obtaining
External Storage write permission. External storage is world
readable, allowing for 'adb pull' on benchmark results on
non-userdebug devices.
- NNScoringTest appends results into app-local csv file,
which is then copied to external storage. This is requierd because
appending to file doesn't work reliably on external storage on
some devices.
- build_and_run_benchmark.sh detects release image, and
asks user to disable display sleep, it also prompts user
to grant MLTS permission for external storage write.
- Added external storage write tests in NNControls and
NNScoringTest tests.
- Remove dead CSV dump code from NNControls

Test: build_and_run_benchmark.sh on userdebug and release devices
Bug: 115720411
Change-Id: I2cc6bf9d944eefa1ca30a107d194078725010fa9
Merged-In: I2cc6bf9d944eefa1ca30a107d194078725010fa9
(cherry picked from commit 3180246f74ade723924cae4ea31eddbfefe09130)
6 files changed