Add a retry to the Swift download in the Dockerfile (#590)

* Add a retry to the Swift download in the Dockerfile.

* Attempting to recover via a manual check of the curl return code.

* Add semicolons.

Author: BradLarson

docker/Dockerfile

@@ -5,8 +5,11 @@ ARG swift_tf_url=https://storage.googleapis.com/swift-tensorflow-artifacts/night
 
 # Download and extract S4TF
 WORKDIR /swift-tensorflow-toolchain
-RUN curl -fSsL $swift_tf_url -o swift.tar.gz \
-    && mkdir usr \
+RUN if ! curl -fSsL --retry 5 $swift_tf_url -o swift.tar.gz; \
+    then curl -fSsL --retry 5 $swift_tf_url -o swift.tar.gz; \
+    fi;
+
+RUN mkdir usr \
     && tar -xzf swift.tar.gz --directory=usr --strip-components=1 \
     && rm swift.tar.gz
 ENV PATH="/swift-tensorflow-toolchain/usr/bin:${PATH}"