replace basetring/xrange

basetring --> six.string_types
xrange --> six.moves.xrange

Partial Implement: blueprint tempest-py33-support

Change-Id: Ia7ae4415d6d4ca9ee04e6735b2c6a6131c05a04f
diff --git a/tempest/stress/driver.py b/tempest/stress/driver.py
index 3715636..9660081 100644
--- a/tempest/stress/driver.py
+++ b/tempest/stress/driver.py
@@ -17,6 +17,8 @@
 import signal
 import time
 
+from six import moves
+
 from tempest import clients
 from tempest.common import ssh
 from tempest.common.utils import data_utils
@@ -128,7 +130,7 @@
             manager = admin_manager
         else:
             manager = clients.Manager()
-        for p_number in xrange(test.get('threads', default_thread_num)):
+        for p_number in moves.xrange(test.get('threads', default_thread_num)):
             if test.get('use_isolated_tenants', False):
                 username = data_utils.rand_name("stress_user")
                 tenant_name = data_utils.rand_name("stress_tenant")