Add BstatsTestApp to instrumentation_test_list.

This app is needed for
FrameworksCoreTests:com.android.internal.os.BatteryStatsValidationTest.

Bug: 69131035
Test: make -j32 continuous_instrumentation_tests dist && verified the test apk is
      available in out/dist/<target>-continuous_instrumentation_tests-<userId>.zip

Change-Id: Ibc274e13d11dabcf184adb8574ab6244cc4f3108