Update GPG key per documentation (#1206)

Author: jplotts

Dockerfile.tmpl

@@ -53,6 +53,10 @@ RUN pip uninstall -y horovod && \
     /tmp/clean-layer.sh
 {{ end }}
 
+# Update GPG key per documentation at https://cloud.google.com/compute/docs/troubleshooting/known-issues
+RUN curl https://packages.cloud.google.com/apt/doc/apt-key.gpg | sudo apt-key add -
+RUN curl https://packages.cloud.google.com/apt/doc/apt-key.gpg | sudo apt-key --keyring /usr/share/keyrings/cloud.google.gpg add -
+
 # Use a fixed apt-get repo to stop intermittent failures due to flaky httpredir connections,
 # as described by Lionel Chan at http://stackoverflow.com/a/37426929/5881346
 RUN sed -i "s/httpredir.debian.org/debian.uchicago.edu/" /etc/apt/sources.list && \