Add check in cloud preprocessor for running on non-cloud

[google]

Add check in cloud preprocessor for running on non-cloud

[aarontp]

For now this check is done in turbiniactl. See #126.

[aarontp]

I think the fix implemented in #126 is actually good enough for most cases, so I'm putting this as a P3. The only thing that a check on the worker itself would add is that it could catch some mis-configurations (workers on a local machine somehow connected to a turbinia instance that is configured for the cloud).

[aarontp]

In practice the client-side checks have been good enough. Closing this as P4 since it would be a nice to have, but realistically not going to get to it at the moment. Maybe once we have more clients sending different types of evidence this would be more important.