SpringBoot CouchbaseReactiveHealthIndicator uses blocking API to retrieve the cluster diagnostics

Title pretty much says it all, but use non-blocking cluster.reactive().diagnostics() instead of blocking cluster.diagnostics() call

Comment From: pivotal-cla

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Comment From: pivotal-cla

@micopiira Thank you for signing the Contributor License Agreement!

Comment From: snicoll

@micopiira thank you for making your first contribution to Spring Boot.