modify longevity summary output

Change-Id: I8c37eec127cab4fbfc0eeefc9eb0465a160e3298
Signed-off-by: Zhu Fangfang <fzhu@rbcon.com>
Reviewed-on: http://reviews.cloudfoundry.org/13022
Tested-by: CI Master <cf-ci@rbcon.com>
Reviewed-by: Pin Xie <pxie@vmware.com>