Check json initial points for unitialized variables

[adowling2]

The idea originates in the #81 discussion.

When the underlying IDAES model changes, the initial points saved as part of the examples become stale. This can cause unexpected long solve times which are challenging to track down the root cause.

[ksbeattie]

@adowling2 This didn't make it for the Aug release, so I'm not moving this to the Nov release and adding it to the backlog label.