Raise StateError on missed variables.

[proofit404]

People should not use hasattr to set user attribute from three tries. Choice different names for different situations.

1. Inside story steps.

   def a1s1(self, state):
       state.foo # error
   

2. Outside of story execution

   state = State()
   state.foo # error
   

3. hasattr should not work

   hasattr(state, 'foo') # error