Hard to run integration tests within an IDE

We assume that people run tests through `make integration`. But @PriyaModali was trying to run an integration test from within her IDE but was encountering unexpected behaviour as her tests were using a stale Skaffold binary.

The issue is that the Skaffold launch helper looks for the `skaffold` binary in the `PATH`. I added the ability to pull a particular binary using the `SKAFFOLD_BINARY` environment variable (#4353).

https://github.com/GoogleContainerTools/skaffold/blob/1f200b186c4a28858b39e9f8e689d5606946fca1/integration/skaffold/helper.go#L302-L306

But it would be really helpful is to have this helper be able to `go run .../cmd/skaffold` so that we never hit a stale binary?