Enable local import of performance_test libs via relative path in quickstart_stress_test.py

Bug: 294879960
Test: python3 quickstart_stress_test.py -c local_dev_testbed.yml -tb LocalUS2GTestBed
Change-Id: I9966a206ac8b42eda2295466745e308705701882
diff --git a/tests/bettertogether/quickstart/performance_test/quick_start_stress_test.py b/tests/bettertogether/quickstart/performance_test/quick_start_stress_test.py
index 117a46a..7e5a49f 100644
--- a/tests/bettertogether/quickstart/performance_test/quick_start_stress_test.py
+++ b/tests/bettertogether/quickstart/performance_test/quick_start_stress_test.py
@@ -15,13 +15,21 @@
 """Stress tests for Neaby Connections used by the quick start flow."""
 
 import datetime
+import os
 import logging
+import sys
 import time
 
 from mobly import asserts
 from mobly import base_test
 from mobly import test_runner
 
+# Allows local imports to be resolved via relative path, so the test can be run
+# without building.
+_performance_test_dir = os.path.dirname(os.path.dirname(__file__))
+if _performance_test_dir not in sys.path:
+  sys.path.append(_performance_test_dir)
+
 from performance_test import nc_base_test
 from performance_test import nc_constants
 from performance_test import nearby_connection_wrapper
@@ -478,4 +486,3 @@
 
 if __name__ == '__main__':
   test_runner.main()
-