fix(Store): Handling of @ngrx/store/update-reducers Action on Startup leads to strange behaviour for initialStates

[berthertogen]

• assign the new state to the overall initial state instead of returning the new state only
• Add test to simulate the following situation:
  Module MA and MB with initial state IA and IB in module.
  Overall initial state RootIAB { IB } with only state of MB being
  initiated.
  When action '@ngrx/store/update-reducers' is fired for MA the RootIAB should be merged with IA so we don't lose the IB initialization in RootIAB.
• Fixed failing test to expect 0 instead of undefined.

Closes #906

[coveralls]

Coverage remained the same at 93.533% when pulling 0f31877 on berthertogen:issue-branch-906 into f17a032 on ngrx:master.

[MikeRyanDev]

If I'm understanding this change correctly it won't be possible to remove state keys by removing reducers, right? I'm not sure if I want to merge in the fix if that's the reprecussion.

The harder fix would be to change the way the Store bootstraps itself. Technically it could load all forFeature() calls that exist in the same injector and resolve them right away as part of the root module. That way you don't get update-reducers calls on bootstrap, only for lazy loaded modules.

[Bretto]

What's the status on this ? Should we worry about all the @ngrx/store/update-reducers in the console ? Once the feature modules are loaded we don't get those actions fired multiple times only the first time. Thanks