Proposed improvements for G_SLICE (#1697)

* Try to fix mamba under aarch64 QEMU by setting ENV G_SLICE=always-malloc

* Set G_SLICE inside if statement

* Write "extract_threads: 1" to /opt/.condarc

Co-authored-by: Ayaz Salikhov <mathbunnyru@gmail.com>

tensorflow-notebook/Dockerfile

@@ -11,7 +11,13 @@ LABEL maintainer="Jupyter Project <jupyter@googlegroups.com>"
 SHELL ["/bin/bash", "-o", "pipefail", "-c"]
 
 # Install Tensorflow
-RUN mamba install --quiet --yes \
+RUN arch=$(uname -m) && \
+    if [ "${arch}" == "aarch64" ]; then \
+        # Prevent libmamba from sporadically hanging on arm64 under QEMU
+        # <https://github.com/mamba-org/mamba/issues/1611>
+        export G_SLICE=always-malloc; \
+    fi && \
+    mamba install --quiet --yes \
     'tensorflow' && \
     mamba clean --all -f -y && \
     fix-permissions "${CONDA_DIR}" && \