rake service optionally

Change-Id: If458c98fef541c7451102ff9194a9614e1c1bc14
Signed-off-by: Zhu Fangfang <fzhu@rbcon.com>
Reviewed-on: http://reviews.cloudfoundry.org/13127
Tested-by: CI Master <cf-ci@rbcon.com>
Reviewed-by: Michael Zhang <zhangcheng@rbcon.com>