Set the DeploymentStrategy to Recreate

[jsanda]

Fixes #63

[sonarcloud]

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[jsanda]

On a new install this gives the desired behavior. I updated the podTemplateSpec of the Deployment and the current replica was deleted before a new one was created.

I also tested by installed k8ssandra 1.0 and then upgrading with changes in k8ssandra/k8ssandra#1044. The update was rolled out and then the operator changed the deployment strategy. We build the desired deployment, compare its resource hash against the actual deployment, and if they differ we copy several properties from the desired deployment into the actual deployment. In the case of the upgrade both the podTemplateSpec and deploymentStrategy are updated at the same time, and based on my testing it appears that the deployment controller first rolls out the update and then updates the deploymentStrategy.

I suppose we could first check to see what the deployment strategy is. If it is RollingUpdate (the default) then we change it to Recreate, and then apply a patch. If the patch is successful we then proceed with the rest of the updates.

@burmanm what do you think about the approach? I'd like a second set of eyes on this.

[burmanm]

In Reaper's case this workaround will probably work just fine as long as there's a single instance limitation.