on timeout, raise dedicated Timeout exception

Change-Id: I085a52194dde0f5e6dd845ffde1197f7dc83b306
diff --git a/src/osmo_gsm_tester/suite.py b/src/osmo_gsm_tester/suite.py
index 94c3882..2313ae2 100644
--- a/src/osmo_gsm_tester/suite.py
+++ b/src/osmo_gsm_tester/suite.py
@@ -24,6 +24,9 @@
 from . import config, log, template, util, resource, schema, ofono_client, osmo_nitb
 from . import test
 
+class Timeout(Exception):
+    pass
+
 class SuiteDefinition(log.Origin):
     '''A test suite reserves resources for a number of tests.
        Each test requires a specific number of modems, BTSs etc., which are
@@ -262,7 +265,7 @@
 
     def wait(self, condition, *condition_args, timeout=300, timestep=1, **condition_kwargs):
         if not self._wait(condition, condition_args, condition_kwargs, timeout, timestep):
-            raise RuntimeError('Timeout expired')
+            raise Timeout('Timeout expired')
 
     def sleep(self, seconds):
         assert seconds > 0.