Add a model loading/unloading stress test

To ensure stability of NNAPI, for every model, this test continuously loads
the model for 30 minutes without doing any inference.

Bug: 123042197
Test: build_and_run_benchmark.sh model-loading-stress
Merged-In: I6b8522b627092e7cafb8370037aa5d66d71f76aa
Change-Id: I6b8522b627092e7cafb8370037aa5d66d71f76aa
(cherry picked from commit 9b6f86f5ae088f03f95c9d1e52e1db0cefefdb99)
4 files changed