Because of the way in which we rebase and build our kube fork, the
binary doesn't have minor versions set correctly. For example, version
1.29.5 appears as `v1.29.0-rc.1.3970+87992f48b0ead9-dirty` and that
breaks the version detection in our scripts.
Since we already have pre-built binaries in CI/release, there is no
reason for downloading those binaries. The only case in which it's
needed is for local dev. So we introduce an env var `SKIP_ENVTEST` to
skip the download when building images.
We cannot execute cross-compiled binaries, otherwise we get an error saying:
```
hack/build-cluster-api.sh: line 26: /go/src/github.com/openshift/installer/cluster-api/bin/darwin_amd64/kube-apiserver: cannot execute binary file: Exec format error
```
The check should be skipped in those cases.
Only download the binaries if the existing binaries' version is lower
than the minimum version (currently 1.28.0). This change will be needed
when we copy etcd/kas binaries from existing container images which
build them from source.
