Add option to write out variable names before history write to catch problems in the write

We sometimes have problems like #1545 where the model fails writing history variables. It would be easier to identify which fields fail if there was a write to the log file just before for which field it's currently writing. This would be an option you would turn on with a namelist flag. With a name say something like

hist_debug_write

And important part of this would be that it do a "sys_flush" after the write, and that it do it from every processor.