Android testing CI faliing (all platforms)

Android Testing CI has been failing for many days, and thus it's been difficult to diagnose issues with it failing with Bazel@HEAD

[Here](https://buildkite.com/bazel/bazel-at-head-plus-downstream/builds/1368#3a7fa3e7-5af6-4902-aba9-032104d467a8) is a failure for Unbuntu 16 this morning using Bazel@HEAD:
```
(02:09:03) ERROR: missing input file 'external/androidsdk/build-tools/28.0.2/lib/dx.jar', owner: '@androidsdk//:build-tools/28.0.2/lib/dx.jar'
--
  | (02:09:03) ERROR: /var/lib/buildkite-agent/.cache/bazel/_bazel_buildkite-agent/d3e6522be4da9d904ab54b448eb64f5e/external/androidsdk/BUILD.bazel:8:1: @androidsdk//:dx_jar_import: missing input file '@androidsdk//:build-tools/28.0.2/lib/dx.jar'
```

I think this dependency was updated in a recent commit?

https://buildkite.com/bazel/android-testing

Comienza con el fallo vinculado de pruebas de Android de Buildkite e inspecciona los registros de Bazel@HEAD en busca de la entrada faltante external/androidsdk/build-tools/28.0.2/lib/dx.jar. Lee external/androidsdk/BUILD.bazel en la ruta de caché referenciada y compara la configuración de dependencias de Android SDK. Se considera terminado cuando Android Testing CI pasa en todas las plataformas afectadas sin el error de dx.jar faltante.

Escrito por el modelo de indexación a partir del texto del issue.