Lint fixes for fb_fstab

[jaymzh]

Rubocop fixes - just keeping everything in sync for easy diffing

Mostly whitespace, but there is a split fix worth checking. See comment here I made on relevent historical commit:

https://github.com/facebook/chef-cookbooks/commit/4b72e8958c52b1579c7e9f99c10187618149e095#r66196415

[facebook-github-bot]

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