Replace xrange() with six.moves.range()

Add "from six.moves import range" to replace the builtin range()
function with six.moves.range() to always create an iterator, instead of
creating a temporary list.

Replace "xrange" with "range".

Don't add the import for ranges of 1024 items or less.

Blueprint cinder-python3
Change-Id: If618b4e810e444f7eb6592bb2398805e9d14d548

cinder/volume/utils.py

@@ -24,6 +24,7 @@ from oslo_log import log as logging
 from oslo_utils import strutils
 from oslo_utils import timeutils
 from oslo_utils import units
+from six.moves import range
 
 from cinder.brick.local_dev import lvm as brick_lvm
 from cinder import db
@@ -443,7 +444,7 @@ def generate_password(length=16, symbolgroups=DEFAULT_PASSWORD_SYMBOLS):
 
     # then fill with random characters from all symbol groups
     symbols = ''.join(symbolgroups)
-    password.extend([random.choice(symbols) for _i in xrange(length)])
+    password.extend([random.choice(symbols) for _i in range(length)])
 
     # finally shuffle to ensure first x characters aren't from a
     # predictable group