IMPALA-11973: Add absolute_import, division to all eligible Python files

This takes steps to make Python 2 behave like Python 3 as
a way to flush out issues with running on Python 3. Specifically,
it handles two main differences:
 1. Python 3 requires absolute imports within packages. This
    can be emulated via "from __future__ import absolute_import"
 2. Python 3 changed division to "true" division that doesn't
    round to an integer. This can be emulated via
    "from __future__ import division"

This changes all Python files to add imports for absolute_import
and division. For completeness, this also includes print_function in the
import.

I scrutinized each old-division location and converted some locations
to use the integer division '//' operator if it needed an integer
result (e.g. for indices, counts of records, etc). Some code was also using
relative imports and needed to be adjusted to handle absolute_import.
This fixes all Pylint warnings about no-absolute-import and old-division,
and these warnings are now banned.

Testing:
 - Ran core tests

Change-Id: Idb0fcbd11f3e8791f5951c4944be44fb580e576b
Reviewed-on: http://gerrit.cloudera.org:8080/19588
Reviewed-by: Joe McDonnell <joemcdonnell@cloudera.com>
Tested-by: Joe McDonnell <joemcdonnell@cloudera.com>

infra/python/bootstrap_virtualenv.py

@@ -32,7 +32,7 @@
 # This module can be run with python >= 2.7. It makes no guarantees about usage on
 # python < 2.7.
 
-from __future__ import print_function
+from __future__ import absolute_import, division, print_function
 import glob
 import logging
 import optparse