* Remove apt package lists and make macro to clean up apt and python cache
Remove the apt package lists (`/var/lib/apt/lists`) from the docker
containers. This saves about 100MB.
Also, make a macro to clean up the apt and python cache that can then be
used in all of the containers. This helps make the cleanup be consistent
across all containers.
Signed-off-by: Saikrishna Arcot <sarcot@microsoft.com>
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