IMPALA-11976: Fix use of deprecated functions/fields removed in Python 3

Python 3 moved several things around or removed deprecated
functions / fields:
 - sys.maxint was removed, but sys.maxsize provides similar functionality
 - long was removed, but int provides the same range
 - file() was removed, but open() already provided the same functionality
 - Exception.message was removed, but str(exception) is equivalent
 - Some encodings (like hex) were moved to codecs.encode()
 - string.letters -> string.ascii_letters
 - string.lowercase -> string.ascii_lowercase
 - string.strip was removed

This fixes all of those locations. Python 3 also has slightly different
rounding behavior from round(), so this changes round() to use future's
builtins.round() to get the Python 3 behavior.

This fixes the following pylint warnings:
 - file-builtin
- long-builtin
- invalid-str-codec
- round-builtin
- deprecated-string-function
- sys-max-int
- exception-message-attribute

Testing:
 - Ran cores tests

Change-Id: I094cd7fd06b0d417fc875add401d18c90d7a792f
Reviewed-on: http://gerrit.cloudera.org:8080/19591
Reviewed-by: Joe McDonnell <joemcdonnell@cloudera.com>
Tested-by: Joe McDonnell <joemcdonnell@cloudera.com>

lib/python/impala_py_lib/gdb/impala-gdb.py

@@ -49,8 +49,8 @@ def get_fragment_instances():
                 # No valid thread_debug_info
                 if not tdi:
                     break
-                hi = long(tdi['instance_id_']['hi'])
-                lo = long(tdi['instance_id_']['lo'])
+                hi = int(tdi['instance_id_']['hi'])
+                lo = int(tdi['instance_id_']['lo'])
                 fi = "%lx:%lx" % (hi, lo)
                 if fi != "0:0":
                     fragment_instances[fi.strip('"')].append(thread.num)