Initial VTS tests for Neural Networks HAL.

This CL has the basic framework for the NNAPI VTS tests with one
positive function test for each HAL function. This CL is being uploaded
now because the NN API HAL files are being moved to hardware/interfaces.

Bug: 63905942
Bug: 63525563
Test: mm -j40
Test: vts-tradefed runs and passes
Change-Id: I8f3d606ec50a6a6d110c89132e6fb89f53f3bf48