* Use version to determine plugin protocol to use
* Remove field from ServeOpts
* Fix missing assignment, handle errors
* contraint -> constraint
* Inject the version string from the vault side
* Fix the version check
* Add grpc support check to database plugins
* Default to use grpc unless missing env var or fail on contraint check
* Add GRPCSupport test
* Add greater than test case
* Add go-version dep
