(maint) Fix running of ssh-agent for acceptance tests
(maint) Fix running of ssh-agent for acceptance tests

Previous commit was starting ssh-agent but its SSH_AGENT_PID and SSH_AUTH_SOCK
values were not being properly exported and ssh-add was not finding the ssh-agent instance.
This fix has Rake parse the output of ssh-agent and add its values to ENV

puppetlabs/pxp-agent,puppetlabs/pxp-agent,puppetlabs/pxp-agent