Add OS specific variable overrides.

[adamus1red]

Specific example is Alpine where the repos use docker rather than docker-ce or docker-ee

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[adamantike]

In case this approach gets approved, it could also include an Archlinux.yml file with docker_package: "docker" too.

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This pull request has been marked 'stale' due to lack of recent activity. If there is no further activity, the PR will be closed in another 30 days. Thank you for your contribution!

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[adamantike]

I would really appreciate if this can be reviewed, considering that is the only missing change for this role to work out of the box with Arch Linux based distros (otherwise, docker_package has to be set to "docker").

[geerlingguy]

I've merged this in to make it more convenient for Arch/Alpine users, but note that precedence means it could be harder for end users to override any vars defined in these included files. So use them sparingly—it makes the role a tiny bit less flexible while also making some platforms better supported OOTB.

@adamantike - if you want to add in a separate PR to add Arch support I'd be willing to merge it (make sure to add to meta/main.yml the new platform, and make sure the name of the file is correct with correct capitalization (not sure if ArchLinux, Arch, or Archlinux)).