kola: stop treating `scos` and `rhcos` as the same distro

[dustymabe]

We should probably unwind the binding:

coreos-assembler/mantle/cmd/kola/options.go

Lines 363 to 370 in 4ed662a

	if kola.Options.Distribution == "" {
	kola.Options.Distribution = kolaDistros[0]
	} else if kola.Options.Distribution == "scos" {
	// Consider SCOS the same as RHCOS for now
	kola.Options.Distribution = "rhcos"
	} else if err := validateOption("distro", kola.Options.Distribution, kolaDistros); err != nil {
	return err
	}

So that we can do things like exclusively run a test just on rhcos and not on scos.

For an example see #4554 where we had to workaround this behavior. The test has Distros: []string{"rhcos"} but the test still ran on scos, which wasn't what we wanted.

[nikita-dubrovskii]

There was a PR some time ago, where i've separeted scos and rhcos, can update and reopen it.