Fix path logic

[yinweisu]

Issue #, if available:

Description of changes:

• Tabular: Fix crash when save path is absolute #3288 introduce logic for saving relative paths for models. This logic affects timeseries too and Trainer in timeseries is not being updated with the relative path logic. This could be an issue in some edge cases, for example:

`current_working_dir` is `/home/ubuntu/user/test`
`path` specified to predictor is `/home/ubuntu/timeseries`

`model_paths` after training will contain `../timeseries/model/XXX`
while the `path` being saved in trainer is `/home/ubuntu/timeseries`
Then when we try to find common prefix to reset the context, it fails as there's no common prefix

Convert trainer's `path` to be relative like what `TabularPredictor` should solve the problem

• Note this is a temp fix and should be removed after the path logic rework: [Tabular] Improve path logic #3260

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[Innixma]

LGTM!

[github-actions]

Job PR-3293-c6baacd is done.
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