suite: Set suite subdir lib part of syspath so tests can import their own modules

Change-Id: I3307c3ab314bb7a88d3c22c7c270c9f05fe6e03e
diff --git a/src/osmo_gsm_tester/suite.py b/src/osmo_gsm_tester/suite.py
index a7f91c5..44aabbd 100644
--- a/src/osmo_gsm_tester/suite.py
+++ b/src/osmo_gsm_tester/suite.py
@@ -148,9 +148,11 @@
         self.reserved_resources = self.resources_pool.reserve(self, self.resource_requirements())
 
     def run_tests(self, names=None):
+        suite_libdir = os.path.join(self.definition.suite_dir, 'lib')
         try:
             log.large_separator(self.trial.name(), self.name(), sublevel=2)
             self.mark_start()
+            util.import_path_prepend(suite_libdir)
             MainLoop.register_poll_func(self.poll)
             if not self.reserved_resources:
                 self.reserve_resources()
@@ -177,6 +179,7 @@
             self.objects_cleanup()
             self.free_resources()
             MainLoop.unregister_poll_func(self.poll)
+            util.import_path_remove(suite_libdir)
             self.duration = time.time() - self.start_timestamp
 
             passed, skipped, failed = self.count_test_results()