fix bugs of search_params;

[Gordon119]

What does this PR do?

Fix some bugs in search_params.py:

1. Test result won't dump to log.
2. Logging message is the same for retrain and no retrain.

Test CLI & API (bash tests/autotest.sh)

Test APIs used by main.py.

• Test Pass
  • All tests finished (13/13) on fix-search_params.py-bugs. See test_report.txt for details.
• Not Applicable (i.e., the PR does not include API changes.)

Check API Document

If any new APIs are added, please check if the description of the APIs is added to API document.

• API document is updated (linear, nn)
• Not Applicable (i.e., the PR does not include API changes.)

Test quickstart & API (bash tests/docs/test_changed_document.sh)

If any APIs in quickstarts or tutorials are modified, please run this test to check if the current examples can run correctly after the modified APIs are released.