clubb stats history fields jumbled for threaded runs

Writing the internal clubb stats vars to the CAM history output produces jumbled arrays for threaded runs. These stats vars are invoked through a two step process (1) add specific vars to the master field list by defining them in namelist ```clubb_vars_zt``` and ```clubb_vars_zm```, and (2) add them to fincl's so they are included in cam history. For example, this is what the field "thlm" looks like running the FV dycore:

The FV dycore defaults to NTHRDS=3. Running w/ NTHRDS=1, the "thlm" field looks correct. Running with the SE dycore (which is always run with NTHRDS=1), the fields look correct as well. So the array jumbling seems to occur for multiple thread runs only.

@Katetc tells me that the next clubb externals update will bring in these vars in a more official way, as an argument to the clubb interface. Currently these vars sneak in to the CAM history output via the internal clubb code, which is likely why it doesn't work for any arbitrary CAM configuration. We should then make sure to resolve this issue when bringing in the new clubb externals.

For now, I have no problem running w/o threading ... and I doubt many users even use this functionality since it's poorly/not documented.