Plumbing to optionally build for arm64

[courtland]

What this PR does / why we need it:

Adds the ability to optionally build binaries for arm64 by setting GOARCH via Makefile variable overrides.

For example:

make GOARCH=arm64 build

make GOARCH=arm64 docker-build

Also fixes the non-dockerized install-go script to correctly download/install the versioned golang under an arm64 host.

Combined, this permits building the plugin(s) for arm64 and/or x86 on either type of host.

Special notes for your reviewer:

Related to #260

Release note:

Ability to build arm64 binaries

[kubevirt-bot]

Hi @courtland. Thanks for your PR.

I'm waiting for a k8snetworkplumbingwg member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[phoracek]

/retest

[phoracek]

Hey @courtland, thanks for submitting this. The dockerized tests have failed. Would you please check it?

[courtland]

It looks like the quay.io/fedora/fedora:34-x86_64 no longer exists, I'm guessing since 34 was EOL a while back? It must have been right after I submitted this, because the tests passed for me locally then.

I will raise another issue to fix the tests and then perhaps I can rebase this PR.

[phoracek]

/retest

[phoracek]

/retest

[phoracek]

/lgtm
/approve
/override pull-e2e-ovs-cni

Failed e2e on an unrelated flake

[kubevirt-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: courtland, phoracek

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