instanceProvider's NeedsUpdate returns false positives in some circumstances

[njvrzm]

What happened:
When mulitple grafana instances talk to the same plugin process, any time two successive requests come from different instances a new datasource is created. The ProxyOpts for each host are different, so when NeedsUpdated checks to see if the incoming GrafanCfg is different from the cached one, it always returns true if the current request is coming from a different grafana instance than previous request. This happens even if the datasource does not use a proxy.

What you expected to happen:
A datasource that doesn't use ProxyOpts should not be considered to need updating if those ProxyOpts change.

How to reproduce it (as minimally and precisely as possible):

• Create a datasource in dev that is enabled for the apiserver and logs something in its InstanceFactoryFunc. The Amazon Athena datasource is one example.
• Make multiple requests to the datasource
• See in the logs that the factory function is being called repeatedly even though no real config changes have been made.