Update install script hosts information

[yt-fido]

Originally reported by: Matt Turk (Bitbucket: MatthewTurk, GitHub: MatthewTurk)

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This should include:

• Removing old XSEDE hosts
• Adding Gordon, Trestles and any other machines
• Making a note about Ubuntu required packages

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• Bitbucket: https://bitbucket.org/yt_analysis/yt/issue/400

[yt-fido]

Original comment by chummels (Bitbucket: chummels, GitHub: chummels):

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Removing milestone: 2.4 (automated comment)

[yt-fido]

Original comment by Matt Turk (Bitbucket: MatthewTurk, GitHub: MatthewTurk):

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Addressed in https://bitbucket.org/yt_analysis/yt/pull-request/213/add-ubuntu-notes-and-safety-check-to-the