Create 32 chars passwords by default

this will play nicer with our defaults when security compliance is
enabled in Keystone and allow us to use dynamic credentials in tempest.

Also replace upper constraints URL with opendev.org one,
tox_install.sh seems to have troubles with redirects.

Change-Id: Ifec79fdb854b529819a4eecd43c442298ac5e442
Related-Issue: PROD-29305
diff --git a/tempest/lib/common/utils/data_utils.py b/tempest/lib/common/utils/data_utils.py
index c5df590..8daffe9 100644
--- a/tempest/lib/common/utils/data_utils.py
+++ b/tempest/lib/common/utils/data_utils.py
@@ -59,7 +59,7 @@
     return rand_name
 
 
-def rand_password(length=15):
+def rand_password(length=32):
     """Generate a random password
 
     :param int length: The length of password that you expect to set