Move internal helpers to the class that uses them

1. if some helpers are used only by one class, then it needn't
   appear in scenario.manager.py.
2. if some helpers are used outside scenario.manager.py, then it
   shouldn't be defined as internal helpers.

This is to move some internal helpers to the only class that
uses them.

Change-Id: I2543daea8d5e33589ebd909ec31551c77e0faaae
2 files changed