Update support for Amazon Linux 2

[hakman]

Amazon Linux 2 support is broken with Docker packages for CentOS, because of the missing container-selinux dependency. Even if this is added from the CentOS repo, it is missing its own dependencies. Sadly, this is not something that can be easily fixed.

The good news is that Amazon Linux 2 has SELinux disabled by default, so the container-selinux package is not needed. Static binaries for containerd or Docker should run just fine.

#8199 adds support for static binaries for latest containerd and can be used to setup a Kubernetes cluster on Amazon Linux 2 with minor changes.

This PR adds the following changes:

• separates Amazon Linux from CentOS and RHEL to not require installing container-selinux
• updates default containerd version to 1.3.2 (noting to worry, this is targeted for 1.18)
• adds simpler aliases for well known accounts

[hakman]

/cc @rifelpet

[hakman]

/assign @justinsb

[justinsb]

Thanks @hakman - it does feel like there are a few possibly unrelated changes in this PR (introducing Amazon System Linux 2, changing the containerd version, recognizing more aliases), and in general this might in future cause problems with cherry-picks, so it's probably a good idea to split them up into separate PRs. (They're also easier to review so we should be able to merge them faster ;-) )

But in this case they're relatively related, so we should just merge:

/approve
/lgtm

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[hakman]

Indeed, the new aliases could have been a separate PR. Thanks @justinsb :)