Prevent LSF commands encoding warnings

[jtpalmer]

Description

Prevents possibly non-UTF-8 encoded data from being passed to json_encode. Specifically, the commands contained in LSF accounting logs aren't guaranteed to be utf8.

Motivation and Context

This prevent PHP warnings. I think it's a very low risk change.

https://help.xdmod.org/a/tickets/11449

Tests performed

Added new unit test.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project as found in the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.