vine: apply BYTES_TO_MEGABYTES when calculate inuse_cache

[JinZhou5042]

Proposed Changes

• Apply BYTES_TO_MEGABYTES when converting bytes data into megabytes, instead of doing math.

• There is a bug in doing w->resources->disk.total - w->inuse_cache, where the left side is in MB while the right side is in Bytes

Merge Checklist

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