fix local exec error with docs

[jshiwamV]

• terraform destroy fails with local-exec error #102: was not able to reproduce the issue mentioned in here, @jubrad . Although I have broken down one liner command, into a set of commands to prepare kube_config file properly before getting node-claims.
• Will raise more PRs to properly document Pre-requisites.

[alex-hunt-materialize]

I don't see much point in writing the file. How does this fix things?

We should document that they need kubectl, though.

[alex-hunt-materialize]

This trap line should happen before the write on the line above.
The file name should also be quoted inside the trap command.

[jshiwamV]

yeah, i kinda guessed if doing everything in one line is causing the issue. I will wait for @jubrad to reply, incase he knows exact steps to repro this. Otherwise i would just get rid of this file change.