Avoid updating cluster spec when changes haven't occured

In general this will help to avoid making unnecessary api calls.
This also creates an issue within openshift where the spec cannot be edited if another writer updates the spec. 

Couchbase cluster cb-qaorgg has changed since you started editing it. You'll need to copy any changes you've made and edit the couchbase cluster again.

I've gone through openshifts web-ui code and wasn't able to work around this because the revisionNumber has to be provided in the update spec.