* Switches out Unhealthy bool for OkUntil timestamp
* Make sure servers are healthy forever if there are no health checks
* Moves health check off into a go routine to avoid blocking conditions
* Improved logging info
* Fixes initial date
* Fixes health checking; alters tests to adapt to async health checking
* Moves future variable into static upstream and populates it in more places
* Restores silencing of stdout during testing
* Restores silencing of stdout during testing
* keeps check url string once built
* Removes debug message
* uses zero value to signal no checking; reduces in-mutex code to a fetch
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