Don't throw exception if base dir missing

lib/worker_multibuild.py

@@ -108,6 +108,8 @@ def list_jobs(directory=".buildbot"):
     """
     results = []
     files = ["Dockerfile", "build.sh", "test.sh"]
+    if not exists(directory):
+        return results
     for item in listdir(directory):
         print("checking directory {}".format(item))
         flag = False