Simplify package name handling

[ekohl]

f614db2 removed the use of $rubygem_katello_ostree variable, but not its definition.

We also don't want to hard fail because we sometimes want to compile on other distros. The most common use case is CI testing our installer by running it with --help. Since that happens on Travis (which is Ubuntu) it hard fails.

[chris1984]

LGTM

[ehelms]

Looks like some new test failures:

Failure/Error: it { expect { should contain_class('katello') }.to raise_error(Puppet::Error, /#{facts[:hostname]}: This module does not support osfamily #{facts[:osfamily]}/) }