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The default 10 seconds health polling interval is too frequent for most of
the cases. Now it has been changed to 60s. A new config
health_polling_interval is added to make the interval configurable.
Cloud admin can totally disable the health polling by set a negative value
for the config.
Task: 39795 Story: 2007683
Change-Id: Iad30487b8c119e94ee21d75f53fb86eb23dff365 (cherry picked from commit 8e9df14d)