fix(detect.go): check default location only after distro-specific

[vdice]

Describe your changes

This PR was created to address the following issue:

Context

There may be scenarios where both a default containerd file exists (eg at /etc/containerd/config.toml) as well as a K8s-distro specific location (eg at /etc/k0s/containerd.toml for K0s). A common example case is installing a specific K8s distro directly on to a host (VM or otherwise) that already has the system containerd installed.

Issue

In the original distro detection logic, a map is used to see if a containerd config exists at a known/supported location; if it does, the distro is determined accordingly. However, maps in Golang are unordered. This means the default config may be returned prior to recognizing that there is a distro-specific config also on the host (eg K0s, MicroK8s, etc).

Proposed solution

In this PR, I've split out the default location into its own const, leaving the map to contain only distro-specific locations. We perform a lookup in this distro-specific map and if we fail to find a config with these choices, we finally try the default location.

Alternate

I'm open to alternate approaches. Use of a third-party ordered map didn't look as nice (more code/setup). We could also iterate over a slice, which is ordered/deterministic, but again would require a bit more code (at least another data structure).

Issue ticket number and link

Checklist before requesting a review

• I have performed a self-review of my code
• If it is a core feature, I have added thorough tests.
• I tested the changes with the following distributions:
  • Kind
  • MiniKube
  • MicroK8s
  • K3s
  • K0s
  • Rancher RKE2
  • Azure AKS
  • GCP GKE (Ubuntu nodes)
  • AWS EKS (AmazonLinux2 nodes)
  • AWS EKS (Ubuntu nodes)
  • Digital Ocean Kubernetes