Make dftimewolf directory if non-existent. (log2timeline#322)

Could also just as easily replace the elif with else, as makedirs would make any missing ones.

dftimewolf/lib/exporters/local_filesystem.py

@@ -33,6 +33,7 @@ def SetUp(self, target_directory=None):  # pylint: disable=arguments-differ
       target_directory = tempfile.mkdtemp(prefix='dftimewolf_local_fs')
     elif os.path.exists(target_directory):
       target_directory = os.path.join(target_directory, 'dftimewolf')
+      os.makedirs(target_directory, exist_ok=True)
     self._target_directory = target_directory
 
   def Process(self):