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  
Docstrings should start off with a verb and a statement of what the function does/returns. The original docstring here before the change was in the right form. Could you rework this to be in that form, something like "Return FieldInformation object for the column, without caching".