Expand `tmt.package_managers.PackageManager` with `remove`

[LecrisUT]

I was designing a plan for a package that has a main foo and python3-foo rpms, and I wanted to test the plan without python3-foo installed by testing-farm. The simplest interface for this would be to allow the package manger to remove packages and have an equivalent interface for prepare.install

[happz]

We can definitely add an "uninstall" action to package managers, but how to express "package python3-foo shall be uninstalled". We have require for "shall be present" and recommend for "may be present", but to remove a package, no key yet.

[martinhoyer]

Can't we do "negative" require? Not sure if better than adding a new absent key.

[LecrisUT]

One option would be to allow package to be a str or a dict, the latter accepting name, install/remove and missing for the prepare.install. I don't think we should support test.require, etc. right now, at least not until #3085 is resolved.

[happz]

Ok, so if the idea is to implement this for the prepare/install plugin first, then it shouldn't be too hard. We already have a precedent for not-just-a-string "packages", test require accepts also libraries and file paths, so yep, that wouldn't be new. It would be in prepare/install, but not in general.