ensure only one droplet with given name exists

[varshavaradarajan]

This PR ensures that we throw an error if more than one droplet with the same name exists in the user's account. In doing so, we ensure that node.spec.ProviderID is always set to the right droplet id or is empty. The impact is that this will cause an error when creating or updating load balancers resulting in the provider id cannot be empty error in the ccm log and records a warning on the service object. But, we would have logged the non-unique droplets in the ccm log making it easier to identify cases and fix it. In the long run, we plan to fix this automatically in our backend and prevent droplets with the same name coming up as far as possible.

[varshavaradarajan]

@timoreimann - if the impact (i.e unable to create or update lb) is a huge concern, then we can merge this after we fix the non unique droplet name issue internally

[mo-rieger]

Should we close this PR? @varshavaradarajan @timoreimann

[timoreimann]

Yes, I agree we should close it. Thanks for raising @mo-rieger.