Update cobra to 1.3.0 for kubectl, fixes flag value parsing issue when value contains colon

[brianpursley]

What type of PR is this?

/kind bug

What this PR does / why we need it:

Upgrade Cobra from 1.2.1 to 1.3.0 to fix a bug where bash completions don't work when the kubectl command uses the --context flag to specify a context that contains a colon.

Example:

~ $ kubectl --context foo:bar get pod <TAB>
pod1     pod2

Additionally...

The GenBashCompletionV2() function that is now being used allows for descriptions to be shown for bash completion commands, which I enabled. This is similar to what kubectl does for zsh and fish completions.

Example:

~ $ kubectl <TAB>
alpha          (Commands for features in alpha)
annotate       (Update the annotations on a resource)
api-resources  (Print the supported API resources on the server)
api-versions   (Print the supported API versions on the server, in the form of "group/version")
apply          (Apply a configuration to a resource by file name or stdin)
attach         (Attach to a running container)
auth           (Inspect authorization)
autoscale      (Auto-scale a deployment, replica set, stateful set, or replication controller)
certificate    (Modify certificate resources.)
cluster-info   (Display cluster information)
completion     (Output shell completion code for the specified shell (bash, zsh or fish))
config         (Modify kubeconfig files)
cordon         (Mark node as unschedulable)
cp             (Copy files and directories to and from containers)
...

Which issue(s) this PR fixes:

Fixes kubernetes/kubectl#1157

Special notes for your reviewer:

Does this PR introduce a user-facing change?

Fixed a bug where bash completions for kubectl don't work if you use the --context flag with a context name that contains a colon

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

[k8s-ci-robot]

@brianpursley: This issue is currently awaiting triage.

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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: brianpursley

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[brianpursley]

/hold

for review...

[k8s-ci-robot]

@brianpursley: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-kubernetes-dependencies	8a231e6	link	true	/test pull-kubernetes-dependencies
pull-kubernetes-verify	8a231e6	link	true	/test pull-kubernetes-verify

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository. I understand the commands that are listed here.

[brianpursley]

OK, it seems I may need to update cobra across k/k for this. Let me reconsider. I'll close this PR for now.