End-to-end tests fail on a clean run

Tests are currently broken in CI and locally on a clean run (no cache). Running it a second time causes them to pass.

Reproduction

cd e2e
bazel test //...
bazel clean --expunge
bazel test //... --test_env=ABC=123

Example failure

ERROR: github-mozilla-deepspeech/BUILD.bazel:3:20: Testing //github-mozilla-deepspeech:checkout failed: I/O exception during sandboxed execution: /data_sda/aleter01/cache/bazel/execroot/_main/bazel-out/k8-fastbuild/bin/external/_main~_repo_rules~github-mozilla-deepspeech-0.9.3/checkout/tensorflow/native_client/dotnet/nupkg/lib (No such file or directory)