CI builds fail due to missing go modules

[rosskirkpat]

CI builds fail due to missing go modules. I thought this was originally caused by bumping from 0.3.6 to 0.3.7 of metrics-server but that is not the case.

Step 11/22 : RUN git fetch --all --tags --prune
 ---> Running in 8c7500d122f0
Fetching origin
[91mFrom https://github.com/kubernetes-sigs/metrics-server
 * [new tag]         v0.1.0         -> v0.1.0
 * [new tag]         v0.2.0         -> v0.2.0
[0m[91m * [new tag]         v0.2.1         -> v0.2.1
[0m[91m * [new tag]         v0.3.0         -> v0.3.0
[0m[91m * [new tag]         v0.3.0-alpha.1 -> v0.3.0-alpha.1
[0m[91m * [new tag]         v0.3.1         -> v0.3.1
[0m[91m * [new tag]         v0.3.2         -> v0.3.2
[0m[91m * [new tag]         v0.3.3         -> v0.3.3
[0m[91m * [new tag]         v0.3.4         -> v0.3.4
[0m[91m * [new tag]         v0.3.5         -> v0.3.5
[0m[91m * [new tag]         v0.3.6         -> v0.3.6
[0m[91m * [new tag]         v0.3.7         -> v0.3.7
[0m[91m * [new tag]         v0.4.0         -> v0.4.0
[0m[91m * [new tag]         v0.4.1         -> v0.4.1
[0m[91m * [new tag]         v0.4.2         -> v0.4.2
[0m[91m * [new tag]         v0.4.3         -> v0.4.3
[0m[91m * [new tag]         v0.4.4         -> v0.4.4
[0m[91m * [new tag]         v0.5.0         -> v0.5.0
[0mRemoving intermediate container 8c7500d122f0
 ---> 4ec655bf3b84
Step 12/22 : RUN git checkout tags/${TAG} -b ${TAG}
 ---> Running in e1f6424c28d7
[91mSwitched to a new branch 'v0.3.7'
[0mRemoving intermediate container e1f6424c28d7
 ---> 49f885d91b54
Step 13/22 : RUN go run vendor/k8s.io/kube-openapi/cmd/openapi-gen/openapi-gen.go --logtostderr     -i k8s.io/metrics/pkg/apis/metrics/v1beta1,k8s.io/apimachinery/pkg/apis/meta/v1,k8s.io/apimachinery/pkg/api/resource,k8s.io/apimachinery/pkg/version     -p ${PKG}/pkg/generated/openapi/     -O zz_generated.openapi     -h $(pwd)/hack/boilerplate.go.txt     -r /dev/null
 ---> Running in e966b4745849
[91mvendor/k8s.io/kube-openapi/cmd/openapi-gen/openapi-gen.go:30:2: no required module provides package github.com/spf13/pflag: go.mod file not found in current directory or any parent directory; see 'go help modules'
vendor/k8s.io/kube-openapi/cmd/openapi-gen/openapi-gen.go:32:2: no required module provides package k8s.io/klog: go.mod file not found in current directory or any parent directory; see 'go help modules'
vendor/k8s.io/kube-openapi/cmd/openapi-gen/openapi-gen.go:27:2: no required module provides package k8s.io/kube-openapi/cmd/openapi-gen/args: go.mod file not found in current directory or any parent directory; see 'go help modules'
vendor/k8s.io/kube-openapi/cmd/openapi-gen/openapi-gen.go:28:2: no required module provides package k8s.io/kube-openapi/pkg/generators: go.mod file not found in current directory or any parent directory; see 'go help modules'
The command '/bin/sh -c go run vendor/k8s.io/kube-openapi/cmd/openapi-gen/openapi-gen.go --logtostderr     -i k8s.io/metrics/pkg/apis/metrics/v1beta1,k8s.io/apimachinery/pkg/apis/meta/v1,k8s.io/apimachinery/pkg/api/resource,k8s.io/apimachinery/pkg/version     -p ${PKG}/pkg/generated/openapi/     -O zz_generated.openapi     -h $(pwd)/hack/boilerplate.go.txt     -r /dev/null' returned a non-zero code: 1
make: *** [Makefile:25: image-build] Error 1

[rosskirkpat]

After trying a run with the old 0.3.6 Tag, it appears this isn't caused by bumping to 0.3.7. I'm testing out a build with go modules off to see if that resolves the issue.