Revert "Removes failing symlink to /usr/bin/python3 because that file already exists"

This reverts commit 13fadd3838.

installer/roles/image_build/files/Dockerfile.sdist

@@ -13,6 +13,8 @@ RUN curl --silent --location https://rpm.nodesource.com/setup_8.x | bash -
 RUN yum install -y nodejs
 RUN npm set progress=false
 
+RUN ln -s /usr/bin/python36 /usr/bin/python3
+
 WORKDIR "/awx"
 
 ENTRYPOINT ["/bin/bash", "-c"]