[lldb/Test] Create dir if it doesn't yet exist in getReproducerArtifact

The type test use this method to store the golden output. This currently
fails if the reproducer directory hasn't yet been created.

lldb/packages/Python/lldbsuite/test/lldbtest.py

@@ -696,6 +696,7 @@ class Base(unittest2.TestCase):
         return os.path.join(self.getSourceDir(), name)
 
     def getReproducerArtifact(self, name):
+        lldbutil.mkdir_p(self.getReproducerDir())
         return os.path.join(self.getReproducerDir(), name)
 
     @classmethod