fixed issue with fieldinformation caching

- the mechanism here is to look up information for a field in a set of "tables_by_priority"; if the field is not found in the first table, then the next table would be checked.  
- The last check-in introduced a regression whereby the first failed lookup would fail-fast, instead of progressing to the next in the "tables_by_priority"
- raising the "DoesNotExist" exception signals to the calling function to continue looking for the field.
- eliminated some superfluous logging.

@jmuhlich @gberriz @dwrobel1  
Then you should introduce a new exception class rather than using Exception, and catch that.