CentOS has monit, ruby, and runit

Signed-off-by: Jeffrey Peckham <peckham@pivotallabs.com>
Ensure that stemcell has /etc/sv dir

Signed-off-by: Jeffrey Peckham <peckham@pivotallabs.com>
Test for ruby Psych library

  * needed by bosh_agent

Signed-off-by: Jeffrey Peckham <peckham@pivotallabs.com>
CentOS stemcell has ruby with Psych support

Signed-off-by: Jeffrey Peckham <peckham@pivotallabs.com>