🐛 [release-1.6] Makefile: refactor how govc is built to workaround dependency issues building govc

[chrischdi]

What this PR does / why we need it:

1. Solves issue on release-1.6 jobs:

/home/prow/go/pkg/mod/github.com/vmware/[email protected]/sts/signer.go:38:2: github.com/google/[email protected]: missing go.sum entry for go.mod file; to add it:
	go mod download github.com/google/uuid

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):

Fixes CI for release-1.6 which is completely red.

Special notes for your reviewer:

Regarding 1.:

• On release-1.6 we import a very old version of github.com/vmware/govmomi in hack/tools.
• Together with the other dependencies defined in hack/tools/go.mod, govc (which is part of govmomi) cannot be built anymore because the dependencies refer different versions of github.com/google/uuid.
• Bumping govmomi is also not easily possible on release-1.6 because this would also bump golangci-lint and result in not being able to build govc too.

Because of the above issues and to align with the core CAPI CI tooling, this PR introduces building govc in the same version as used in the top level go.mod without using hack/tools/go.mod, but the hack/go-install.sh script instead.

Please confirm that if this PR changes any image versions, then that's the sole change this PR makes.

Release note:

[chrischdi]

awesome.

We now hit the same issue as on release-1.5 😄

[chrischdi]

/test pull-cluster-api-provider-vsphere-verify-crds

[chrischdi]

Note: the follow-up issue gets solved in #1984, which is this one:

Note: this PR is required to fix CI which is red due to:

Failed to run clusterctl config cluster
Unexpected error:
    <*yamlprocessor.errMissingVariables | 0xc000ccc090>: {
        Missing: [
            "VSPHERE_TLS_THUMBPRINT",
        ],
    }
    value for variables [VSPHERE_TLS_THUMBPRINT] is not set. Please set the value using os environment variables or the clusterctl config file
occurred
/home/prow/go/pkg/mod/sigs.k8s.io/cluster-api/[email protected]/framework/clusterctl/client.go:216}

[randomvariable]

/retest-required
/approve

[k8s-ci-robot]

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[chrischdi]

/test pull-cluster-api-provider-vsphere-verify-gen

[chrischdi]

Still needs a lgtm :-)

[randomvariable]

/lgtm