SLING-3500 - use HealthCheckExecutor in CompositeHealthCheck - contributed by Georg Henzler, thanks!

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1600564 13f79535-47bb-0310-9956-ffa450edef68
SLING-3500 - minor tweaks

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1600565 13f79535-47bb-0310-9956-ffa450edef68