Reduce CI Docker image size #371
Description
cpssd/heracles image is pretty large (docker images cpssd/heracles shows its size as 1.66GB), and it takes between 17-35 seconds to download for CircleCI. We should try and take a look at some more lightweight alternatives.
Alpine is a good choice, it contains the protobuf library, but it by default only has stable toolchain, and creating nightly would be rather problematic due to limited libc support. Also the stable image relies on a lot of patching to make it work.