trial: always use abspath

No actual failure known, but using the abspath will prevent further problems
when running a binary in its own run dir and passing trial paths to it.

Adjust test expectations.

Change-Id: Ia2ba876a42eef9122a92645edd1f28ddb56e6be3
diff --git a/src/osmo_gsm_tester/trial.py b/src/osmo_gsm_tester/trial.py
index a7c74c4..171061d 100644
--- a/src/osmo_gsm_tester/trial.py
+++ b/src/osmo_gsm_tester/trial.py
@@ -52,7 +52,7 @@
             return Trial(trials_dir.child(next_trial)).take()
 
     def __init__(self, trial_dir):
-        self.path = trial_dir
+        self.path = os.path.abspath(trial_dir)
         self.set_name(os.path.basename(self.path))
         self.set_log_category(log.C_TST)
         self.dir = util.Dir(self.path)