Use .runner_config instead of .config

CTS TF started to read subdir .config file converted from AT.xml in the new suite impl.
This conflicts with our runner config's file extension.

Test: run vts-selftest
Bug: 78287777
Change-Id: I6c02f823a18a4f37a7b0547ecba9559cce524319
Merged-In: I6c02f823a18a4f37a7b0547ecba9559cce524319
10 files changed