osmo-gsm-tester: Point config parameter to file instead of its dirname

Since osmo-gsm-tester.git Change-Id Ieca65b71b543c44cfcec8e83efd0fe053c432e55,
the -c parameter holds the config file and not the directory where it is contained.

Change-Id: I9aca57c4dd3180367eb17ec92177b90a9c411a6a
2 files changed