Ensure that "antctl version" always outputs the client version

[antoninbas]

Update antctl command framework to support outputting information to the
user even when a client request to the server (Agent or Controller)
fails. We leverage this framework to ensure that "antctl version" always
outputs the client version.

To test this functionality, we introduce an interface for the "client"
part of antctl, which is in charge of sending a request to the
appropriate server. We mock this interface so it can be used in unit
tests. Although in the Antrea codebase, we typically place mocks in a
sub-package called "testing", it is not possible here, due to the very
flat nature of the antctl package, and to the dependencies between
objects. For example, "commandDefinition" depends on "client" and
"client" depends on "commandDefinition". Changing this structure would
require a large code refactor, so instead we adapt the code generation
framework to exceptionally tolerate placing mocks directly in the
package.

Fixes #1872

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[jianjuns]

Could you paste the example output for me to understand?

[antoninbas]

New anctl behavior:

$ ./bin/antctl-darwin -o json version
{
  "antctlVersion": "v0.14.0-dev-d3473075.dirty"
}
Error: unable to load in-cluster configuration, KUBERNETES_SERVICE_HOST and KUBERNETES_SERVICE_PORT must be defined
$ ./bin/antctl-darwin --kubeconfig ~/vmware/antrea/test/e2e/infra/vagrant/playbook/kube/config -o json version
{
  "controllerVersion": "v0.13.0-dev-85ceb847",
  "antctlVersion": "v0.14.0-dev-d3473075.dirty"
}

And kubectl for comparison:

$ kubectl -o json version
{
  "clientVersion": {
    "major": "1",
    "minor": "20",
    "gitVersion": "v1.20.1",
    "gitCommit": "c4d752765b3bbac2237bf87cf0b1c2e307844666",
    "gitTreeState": "clean",
    "buildDate": "2020-12-18T12:09:25Z",
    "goVersion": "go1.15.5",
    "compiler": "gc",
    "platform": "darwin/amd64"
  }
}
The connection to the server localhost:8080 was refused - did you specify the right host or port?
$ kubectl --kubeconfig ~/vmware/antrea/test/e2e/infra/vagrant/playbook/kube/config -o json version
{
  "clientVersion": {
    "major": "1",
    "minor": "20",
    "gitVersion": "v1.20.1",
    "gitCommit": "c4d752765b3bbac2237bf87cf0b1c2e307844666",
    "gitTreeState": "clean",
    "buildDate": "2020-12-18T12:09:25Z",
    "goVersion": "go1.15.5",
    "compiler": "gc",
    "platform": "darwin/amd64"
  },
  "serverVersion": {
    "major": "1",
    "minor": "20",
    "gitVersion": "v1.20.2",
    "gitCommit": "faecb196815e248d3ecfb03c680a4507229c2a56",
    "gitTreeState": "clean",
    "buildDate": "2021-01-13T13:20:00Z",
    "goVersion": "go1.15.5",
    "compiler": "gc",
    "platform": "linux/amd64"
  }
}

Both exit with code 1 in the error / incomplete case.

[jianjuns]

Thanks for pasting the outputs. LGTM.

[jianjuns]

Is that the Transform func will still be called for the fallback response?

[antoninbas]

correct, I considered several approaches but that's the one I went for: generate a "fake" server response and let it go through the transform functions as usual. An alternative was to modify the transforms to handle nil responses, but that seemed more error-prone, more invasive and less flexible.

[tnqn]

LGTM

[antoninbas]

/test-all