Enable atest for mediatranscoder benchmarks

Bug: 173627260
Test: push libmediatranscoder.so to /system/lib64 (if required)
Test: atest MediaTrackTranscoderBenchmark \
      -- --enable-module-dynamic-download=true
Test: atest MediaTranscoderBenchmark \
      -- --enable-module-dynamic-download=true
Test: atest MediaSampleReaderBenchmark \
      -- --enable-module-dynamic-download=true

Change-Id: I048876ecc884f534d5aeee1c173dcc4cfe838dae
2 files changed