Panic if I try to kube login into a microk8s

[benarent]

Description

What happened:

SIGSEGV, we should provide an error message that is more user friendly

➜  tsh logout
Logged out all users from all proxies.

➜  tsh kube login microk8s
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x148 pc=0x530e18d]

goroutine 1 [running]:
main.(*kubeLoginCommand).run(0xc000224740, 0xc000446f00, 0xa, 0xc00023ba01)
	/private/tmp/build-darwin-amd64/go/src/github.com/gravitational/teleport/tool/tsh/kube.go:239 +0xad
main.Run(0xc00003c090, 0x3, 0x3)
	/private/tmp/build-darwin-amd64/go/src/github.com/gravitational/teleport/tool/tsh/tsh.go:423 +0x63e5
main.main()
	/private/tmp/build-darwin-amd64/go/src/github.com/gravitational/teleport/tool/tsh/tsh.go:208 +0xdd

What you expected to happen:

How to reproduce it (as minimally and precisely as possible):

Environment

• Teleport version (use teleport version):

• Tsh version (use tsh version):

• OS (e.g. from /etc/os-release):

• Where are you running Teleport? (e.g. AWS, GCP, Dedicated Hardware):

Browser environment

• Browser Version (for UI-related issues):
• Install tools:
• Others:

Relevant Debug Logs If Applicable

• tsh --debug
• teleport --debug