signed rpm fetch job should verify the rpms are signed

Currently, the job that fetches the signed devstudio rpms can't automatically verify the rpms are signed because the key is not installed on the slaves.

https://dev-platform-jenkins.rhev-ci-vms.eng.rdu2.redhat.com/view/Devstudio/view/jbosstools-releng/job/jbosstools-releng-push-to-staging-06-sign-rpm-fetch/11/console

So, we need to fix that so that the job can verify signing has occurred and speed up the release process.