Replace underscore with a hyphen for Foreman CLI.

As per https://github.com/theforeman/hammer-cli-foreman/pull/108,
Foreman hammer CLI commands will replace underscores for hyphens.

A separate PR will be filed once Katello CLI goes through the same
changes (see http://projects.theforeman.org/issues/4709).
Merge pull request #527 from omaciel/replace-underscore-with-hyphen

Replace underscore with a hyphen for Foreman CLI.