Adding ssh-keys to the release configurations.

Clean up unused lines of command.

The ssh-agent configuration was tested successfully on a full cycle of Indigo Trust 64 with the keys removed from the slaves. There are other jobs that will not work without the keys. In particular the ssh-agent does not appear to penetrate inside the jenkins_tools chroots.
Merge pull request #177 from ros-infrastructure/add_ssh_agent_credentials

Adding ssh-keys to the release configurations.