Add more cleanup to TPU dockerfile (#1538)

https://chat.kaggle.net/kaggle/pl/ikhh6tgbziru9eyj1m58tdmk9o

Author: tifftoff

tpu/Dockerfile

@@ -28,7 +28,9 @@ ADD patches/kaggle_datasets.py /root/.local/lib/${PYTHON_VERSION_PATH}/site-pack
 # Prereqs
 # This is needed for cv2 (opencv-python):
 # https://stackoverflow.com/questions/55313610/importerror-libgl-so-1-cannot-open-shared-object-file-no-such-file-or-directo
-RUN apt-get update && apt-get install ffmpeg libsm6 libxext6  -y
+RUN /tmp/clean-layer.sh && \
+    apt-get update && apt-get install ffmpeg libsm6 libxext6 -y && \
+    /tmp/clean-layer.sh
 
 # Install all the packages together for maximum compatibility.
 # Additional useful packages should be added in the requirements.txt

tpu/clean-layer.sh

@@ -19,4 +19,12 @@ apt-get clean
 # Ensures the current working directory won't be deleted
 cd /usr/local/src/
 # Delete source files used for building binaries
-rm -rf /usr/local/src/*
+rm -rf /usr/local/src/*
+
+# More clean up to save disk space
+rm -rf /var/lib/apt/lists/*
+find /tmp -mindepth 1 ! -name 'clean-layer.sh' -delete 2>/dev/null || true
+rm -rf /root/.cache
+rm -rf /var/cache/apt/archives/*
+find /usr -name '*.pyc' -delete 2>/dev/null || true
+find /usr -name '__pycache__' -type d -exec rm -rf {} + 2>/dev/null || true