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

Inizia dal fallimento dei test Android collegato di Buildkite e ispeziona i log di Bazel@HEAD alla ricerca dell’input mancante external/androidsdk/build-tools/28.0.2/lib/dx.jar. Leggi external/androidsdk/BUILD.bazel nel percorso della cache indicato e confronta la configurazione delle dipendenze di Android SDK. Il lavoro è completato quando Android Testing CI passa su tutte le piattaforme interessate senza l’errore relativo all’assenza di dx.jar.

Scritto dal modello di indicizzazione a partire dal testo della issue.