Don't hand compute mydir, do it using "TestBase.compute_mydir(__file__)".

llvm-svn: 214575
diff --git a/lldb/test/python_api/signals/TestSignalsAPI.py b/lldb/test/python_api/signals/TestSignalsAPI.py
index 9702284..fd2c820 100644
--- a/lldb/test/python_api/signals/TestSignalsAPI.py
+++ b/lldb/test/python_api/signals/TestSignalsAPI.py
@@ -9,7 +9,7 @@
 from lldbtest import *
 
 class SignalsAPITestCase(TestBase):
-    mydir = os.path.join("python_api", "signals")
+    mydir = TestBase.compute_mydir(__file__)
 
     @python_api_test
     def test_ignore_signal(self):