raised a `SkipException` before into `foreach_execute` when command does not exist

[xiangce]

    @xiangce this exception is raised from a `foreach_execute` that depends on the `block_devices_by_uuid`
      datasource for inputs.  If the command does not exist on a system should the datasource ever execute? 
      Should have raised a `SkipException` before it ever got to the `foreach_execute`?

Originally posted by @bfahr in https://github.com/RedHatInsights/insights-core/issues/3584#issuecomment-1349619401