If the DNS change has not propagated yet to all nameservers, then it may
be that the first reachability success goes through but a second one
falis. in that case we are better off first trying for 'consecutive
success' before we proceed with the deploy

can be used in deploy.php like:
```
$testingStage->addBrancherServer("$APP_NAME")
    ->setLabels(['autodestroy=false', 'stage=acceptance', 'ci_ref=' . (\getenv('GITHUB_HEAD_REF') ?: 'none')])
    ->setBrancherReachabilityCheckCount(6)      // Amount of consecutive checks required
    ->setBrancherReachabilityCheckInterval(10); // Amount of seconds between checks
```

so we can test both PRs without merging both:
ByteInternet/hypernode-deploy-configuration#55
#184

This reverts commit f06be7f.

more robust waitForAvailability