Fix nested TPC-H data loading on python 2.6
Fix nested TPC-H data loading on python 2.6

Element.iter() is only available in 2.7. Both 2.6 and 2.7 have
Element.getiterator(). This change was tested on both python versions.
The full load_nested.py script worked in both cases.

Change-Id: I0475c202e96828e9783207e72955a5e9ba7a01d0
Reviewed-on: http://gerrit.cloudera.org:8080/1860
Reviewed-by: Skye Wanderman-Milne <6d4b168ab637b0a20cc9dbf96abb2537f372f946@cloudera.com>
Tested-by: Internal Jenkins

cloudera/Impala,michaelhkw/incubator-impala,cloudera/Impala,michaelhkw/incubator-impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,michaelhkw/incubator-impala,michaelhkw/incubator-impala,cloudera/Impala,michaelhkw/incubator-impala,michaelhkw/incubator-impala,cloudera/Impala,michaelhkw/incubator-impala