Add Fedora 31, drop Fedora 26

[ekohl]

Fedora 26 is EOL. Fedora 32 is not added since there are no packages available.

[ekohl]

Looks like cron is not available, like in the ubuntu images. I've submitted puppetlabs/puppetlabs-stdlib#1108 which can make our code dynamic rather than having to hardcode available providers. For now I've just ensured the package is installed in our acceptance tests.

[mmoll]

As it seems, there are no puppetserver RPMs available for F31 currently.

[ekohl]

Not entirely sure how to deal with this now. On the one hand, the agent works but on the other, it's not entirely there. We have unsupported_puppetmaster_osfamily but Fedora is not its own family.

[mmoll]

Maybe we can just add a puppetserver_supported variable? Then the Ubuntu/focal PR also could go in and we can enable it per OS, once new puppetserver builds are available...

[ekohl]

So something like this. I added a trivial agent test case to at least test something

[mmoll]

merged, bedankt @ekohl!