Using server groups and node selector causes Operator to incorrectly detect a diff

Summary
When using both server groups and manually specified node selectors for your pods (as recommended in our docs), the Operator will incorrectly detect a diff every reconcile loop.
This will mostly result in huge log spam, functionally the Operator still works correctly but makes debugging/supportability almost impossible as the logs wrap very quickly.

+Steps to Reproduce

1. Create the following cluster (adjusting the serverGroup for what's appropriate for your cluster):

   apiVersion: couchbase.com/v2

   kind: CouchbaseCluster

   metadata:

   name: cb-example

   spec:

   serverGroups:

   - eu-west-2b

   image: couchbase/server:6.5.0

   security:

   adminSecret: cb-example-auth

   buckets:

   managed: true

   servers:

   - size: 1

   name: data

   pod:

   spec:

   nodeSelector:

   kubernetes.io/os: linux

   services:

   - data

2. Wait for the cluster to be setup
3. Review the Operator logs

Expected behavior

Once the cluster has been setup, there shouldn't be any further logging from the Operator as it can bail from the reconcile loop without taking action

Actual behavior
Logs are spammed once a second with messages like:

{"level":"info","ts":1595325880.433218,"logger":"cluster","msg":"Resource updated","cluster":"default/cb-example","diff":"  strings.Join({\n  \t... // 38 identical lines\n  \t\"      containers: null\",\n  \t\"      nodeSelector:\",\n- \t\"        failure-domain.beta.kubernetes.io/zone: eu-west-2b\",\n  \t\"        kubernetes.io/os: linux\",\n  \t\"  resources: {}\",\n  \t... // 6 identical lines\n  }, \"\\n\")\n"}

{"level":"info","ts":1595325881.8336375,"logger":"cluster","msg":"Resource updated","cluster":"default/cb-example","diff":"  strings.Join({\n  \t... // 38 identical lines\n  \t\"      containers: null\",\n  \t\"      nodeSelector:\",\n- \t\"        failure-domain.beta.kubernetes.io/zone: eu-west-2b\",\n  \t\"        kubernetes.io/os: linux\",\n  \t\"  resources: {}\",\n  \t... // 6 identical lines\n  }, \"\\n\")\n"}

Analysis

It seems that the Operator is not taking into account the merging of the Node Selector that it has to do to accomodate server groups when it is generating the diff between the contents of the CouchbaseCluster and the previous one.
This leads it to believe that it's changing every single reconcile loop.
The actual pod has the correct node selectors applied, so it's just an issue with the diffing:

  nodeSelector:

    failure-domain.beta.kubernetes.io/zone: eu-west-2b

    kubernetes.io/os: linux