allow error from kind at image loading to propagate

[balopat]

This came up during integration testing.

Previous output:

 loading images into kind nodes: unable to load image with kind "gcr.io/k8s-skaffold/skaffold-example:ad4adf2213c59a487ebf578f5f67c4a0ba030ac36ce16f4ac6d75f04a273e35f": exit status 1

This PR's output:

 loading images into kind nodes: unable to load image with kind "gcr.io/k8s-skaffold/skaffold-example:6838e8133d96ef77de6d3702179c597411c038cb99de06360a58cbdbac5721f8": running [kind load docker-image --name modified-context gcr.io/k8s-skaffold/skaffold-example:6838e8133d96ef77de6d3702179c597411c038cb99de06360a58cbdbac5721f8]
         - stdout: ""
         - stderr: "ERROR: no nodes found for cluster \"modified-context\"\n"
         - cause: exit status 1, 

[codecov]

Codecov Report

Merging #4196 into master will decrease coverage by 0.01%.
The diff coverage is 100.00%.

Impacted Files	Coverage Δ
pkg/skaffold/runner/kind.go	100.00% <100.00%> (ø)
...affold/kubernetes/portforward/kubectl_forwarder.go	65.85% <0.00%> (-2.44%)	⬇️