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
Change-Id: I9464fe2d9b94d167b3f2654470cb60dee2eb5e81
Merged-In: I9464fe2d9b94d167b3f2654470cb60dee2eb5e81
8 files changed