Since this test requires setup before it can successfully run,
we define it as an integration test and move it here so that on a
fresh checkout a user can always run `go test ./pkg/...` and expect that
it would succeed.
Also involves:
- Exporting the VersionChecker and adding NewWithConfig to enable
testing
- Some comment changes
- A change to the type returned by New(); see
https://github.com/golang/go/wiki/CodeReviewComments#interfaces
Ideally I'd not add `NewFromClient` but I think it's the most minimal
change and is preferable to publicly exporting `VersionChecker.client`.
Signed-off-by: Ashley Davis <ashley.davis@jetstack.io>
