fix mode set to int octal instead of octal notation

[nicholasmhughes]

What does this PR do?

Fixes permissions set incorrectly in transition from full text file management (int octal) to salt.modules.file.set_mode management (octal notation).

Previous Behavior

0644 passed as mode would be converted to 420

New Behavior

0644 is retained through passing to salt.modules.file.set_mode

Merge requirements satisfied?

[NOTICE] Bug fixes or features added to Salt require tests.

• [x] Docs
• [x] Changelog - https://docs.saltproject.io/en/master/topics/development/changelog.html
• [x] Tests written/updated

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Yes

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