Make the zlib-devel package available in CentOS 8 and AmazonLinux2 images

[gwynne]

The intention of this change is to add to out-of-the-box usability for the new eimages and improve consistency between the various platforms. Justifications:

• While not a dependency of Swift at runtime on any OS, the libz headers and libraries are commonly required by widely-used libraries such as swift-nio-extras and Vapor.
• The equivalent zlib1g-dev package is provided by all non-slim Ubuntu images.
• The Docker images resulting from this change were less than 60KB larger in local testing.

[gwynne]

@swift-ci please test

[tomerd]

we have had a bit of a discussion about libz in https://forums.swift.org/t/additional-linux-distributions/

at this point I am not convinced we should add non-core dependencies to our base image (we should look into why ubuntu has it!) given the reasons mentioned in the thread. as a quick example why libz but not libssl which is also needed by many packages

that said, I would be happy to open to a wide discuss more with the community (in the forums) to explore possible solutions

cc @drexin

[tomerd]

we discussed this further in the SSWG meeting and decided to make a one time exception for libz-dev only since while its not strictly required for swift it is already in ubuntu images and removing it from ubuntu will break people builds. iow, the reasoning is for backward compatibility.

cc @shahmishal @drexin @tachoknight

[gwynne]

@swift-ci please test

[gwynne]

Not sure why the CI is failing... It's only failing on images I didn't touch in the first place:

07:47:00 [FAILED] - /home/buildnode/jenkins/workspace/swift-docker-PR-linux/5.0/ubuntu/18.04/slim
07:49:32 [FAILED] - /home/buildnode/jenkins/workspace/swift-docker-PR-linux/5.0/ubuntu/18.04
08:00:36 [FAILED] - /home/buildnode/jenkins/workspace/swift-docker-PR-linux/4.2/ubuntu/16.04
08:05:32 [FAILED] - /home/buildnode/jenkins/workspace/swift-docker-PR-linux/4.0

Is this a known problem?

[shahmishal]

Not sure why the CI is failing... It's only failing on images I didn't touch in the first place:

07:47:00 [FAILED] - /home/buildnode/jenkins/workspace/swift-docker-PR-linux/5.0/ubuntu/18.04/slim
07:49:32 [FAILED] - /home/buildnode/jenkins/workspace/swift-docker-PR-linux/5.0/ubuntu/18.04
08:00:36 [FAILED] - /home/buildnode/jenkins/workspace/swift-docker-PR-linux/4.2/ubuntu/16.04
08:05:32 [FAILED] - /home/buildnode/jenkins/workspace/swift-docker-PR-linux/4.0

Is this a known problem?

This is was due to key server failure (connection issue)