Fix kubepkg options parsing

[saschagrunert]

What type of PR is this?

/kind regression

What this PR does / why we need it:

The custom options where not working at all before because of the
parsing in init(). This as been fixed by making the flag vars global
and the ad-hoc creation of options.Options.

Which issue(s) this PR fixes:

Fixes #1331

Special notes for your reviewer:

None

Does this PR introduce a user-facing change?

- Fixed not working `kubepkg` flag parsing

[justaugustus]

Looks good locally:

$ time kubepkg debs --log-level debug --packages kubelet,kubeadm --arch amd64,arm64 --channels stable --spec-only --cni-version v0.8.7
DEBU Using log level "debug"                       file="cmd/root.go:139"
DEBU Using options: &{buildType:deb revision:0 kubeVersion: cniVersion:v0.8.7 criToolsVersion: packages:[kubelet kubeadm] channels:[stable] architectures:[amd64 arm64] releaseDownloadLinkBase:https://dl.k8s.io templateDir:templates/latest specOnly:true}  file="cmd/root.go:154"
INFO Constructing builds...                        file="kubepkg/kubepkg.go:167"
INFO Successfully constructed builds               file="kubepkg/kubepkg.go:205"
INFO Walking builds...                             file="kubepkg/kubepkg.go:210"
INFO Retrieving Kubernetes release version for release/stable  file="release/version.go:91"
INFO Retrieving Kubernetes build version from https://dl.k8s.io/release/stable.txt...  file="release/version.go:118"
INFO Retrieved Kubernetes version: v1.18.3         file="release/version.go:124"
INFO Kubernetes download link base: https://dl.k8s.io/v1.18.3  file="kubepkg/kubepkg.go:294"
INFO Setting version for kubelet package...        file="kubepkg/kubepkg.go:401"
INFO Using Kubernetes version v1.18.3 for kubelet package  file="kubepkg/kubepkg.go:406"
INFO kubelet package version: 1.18.3               file="kubepkg/kubepkg.go:305"
INFO Getting CNI version...                        file="kubepkg/kubepkg.go:438"
INFO Setting CNI version to v0.8.7                 file="kubepkg/kubepkg.go:453"
INFO Building kubelet package for amd64/amd64 architecture...  file="kubepkg/kubepkg.go:326"
INFO Package specs have successfully been built    file="kubepkg/template.go:82"
INFO Spec-only mode was selected; kubepkg will now exit without building packages  file="kubepkg/kubepkg.go:353"
INFO Retrieving Kubernetes release version for release/stable  file="release/version.go:91"
INFO Retrieving Kubernetes build version from https://dl.k8s.io/release/stable.txt...  file="release/version.go:118"
INFO Retrieved Kubernetes version: v1.18.3         file="release/version.go:124"
INFO Kubernetes download link base: https://dl.k8s.io/v1.18.3  file="kubepkg/kubepkg.go:294"
INFO Setting version for kubeadm package...        file="kubepkg/kubepkg.go:401"
INFO Using Kubernetes version v1.18.3 for kubeadm package  file="kubepkg/kubepkg.go:406"
INFO kubeadm package version: 1.18.3               file="kubepkg/kubepkg.go:305"
INFO Getting CNI version...                        file="kubepkg/kubepkg.go:438"
INFO Setting CNI version to 0.8.6                  file="kubepkg/kubepkg.go:457"
INFO Building kubeadm package for amd64/amd64 architecture...  file="kubepkg/kubepkg.go:326"
INFO Package specs have successfully been built    file="kubepkg/template.go:82"
INFO Spec-only mode was selected; kubepkg will now exit without building packages  file="kubepkg/kubepkg.go:353"
INFO Retrieving Kubernetes release version for release/stable  file="release/version.go:91"
INFO Retrieving Kubernetes build version from https://dl.k8s.io/release/stable.txt...  file="release/version.go:118"
INFO Retrieved Kubernetes version: v1.18.3         file="release/version.go:124"
INFO Kubernetes download link base: https://dl.k8s.io/v1.18.3  file="kubepkg/kubepkg.go:294"
INFO Setting version for kubelet package...        file="kubepkg/kubepkg.go:401"
INFO Using Kubernetes version v1.18.3 for kubelet package  file="kubepkg/kubepkg.go:406"
INFO kubelet package version: 1.18.3               file="kubepkg/kubepkg.go:305"
INFO Getting CNI version...                        file="kubepkg/kubepkg.go:438"
INFO Setting CNI version to v0.8.7                 file="kubepkg/kubepkg.go:453"
INFO Building kubelet package for arm64/arm64 architecture...  file="kubepkg/kubepkg.go:326"
INFO Package specs have successfully been built    file="kubepkg/template.go:82"
INFO Spec-only mode was selected; kubepkg will now exit without building packages  file="kubepkg/kubepkg.go:353"
INFO Retrieving Kubernetes release version for release/stable  file="release/version.go:91"
INFO Retrieving Kubernetes build version from https://dl.k8s.io/release/stable.txt...  file="release/version.go:118"
INFO Retrieved Kubernetes version: v1.18.3         file="release/version.go:124"
INFO Kubernetes download link base: https://dl.k8s.io/v1.18.3  file="kubepkg/kubepkg.go:294"
INFO Setting version for kubeadm package...        file="kubepkg/kubepkg.go:401"
INFO Using Kubernetes version v1.18.3 for kubeadm package  file="kubepkg/kubepkg.go:406"
INFO kubeadm package version: 1.18.3               file="kubepkg/kubepkg.go:305"
INFO Getting CNI version...                        file="kubepkg/kubepkg.go:438"
INFO Setting CNI version to 0.8.6                  file="kubepkg/kubepkg.go:457"
INFO Building kubeadm package for arm64/arm64 architecture...  file="kubepkg/kubepkg.go:326"
INFO Package specs have successfully been built    file="kubepkg/template.go:82"
INFO Spec-only mode was selected; kubepkg will now exit without building packages  file="kubepkg/kubepkg.go:353"
INFO Package specs have been saved in /tmp/kubepkg787923350  file="kubepkg/kubepkg.go:230"
INFO Successfully walked builds                    file="kubepkg/kubepkg.go:232"

Thanks for the quick fix!
/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: justaugustus, saschagrunert

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