cli: Fix var get command incorrectly using modify time as create.

[jrasell]

The command was using the variable modify time as the create time table entry. The command has been updated to now use the correct API data.

The create and modify times both also used different formatting techiques creating subtle output differences. This command has been updated to use the helper function, which ensures both times are formatted in the same way.

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[tgross]

LGTM!