[SPARK-20631][PYTHON][ML] LogisticRegression._checkThresholdConsistency should...

[SPARK-20631][PYTHON][ML] LogisticRegression._checkThresholdConsistency should use values not Params

## What changes were proposed in this pull request?

- Replace `getParam` calls with `getOrDefault` calls.
- Fix exception message to avoid unintended `TypeError`.
- Add unit tests

## How was this patch tested?

New unit tests.

Author: zero323 <zero323@users.noreply.github.com>

Closes #17891 from zero323/SPARK-20631.