Remove unused configuration variables

* from the config sample
* from the config.py
* from the config template

Change-Id: Ic4c57f8c20d3e4107adc3a64b234fe578c4d899c
diff --git a/etc/tempest.conf.tpl b/etc/tempest.conf.tpl
index 880a3c1..8ef5b84 100644
--- a/etc/tempest.conf.tpl
+++ b/etc/tempest.conf.tpl
@@ -181,11 +181,8 @@
 # This section contains configuration options used when executing tests
 # against the OpenStack Object Storage API.
 # This should be the username of a user WITHOUT administrative privileges
-username = %USERNAME%
-# The above non-administrative user's password
-password = %PASSWORD%
-# The above non-administrative user's tenant name
-tenant_name = %TENANT_NAME%
+
+# You can configure the credentials in the compute section
 
 # The type of endpoint for an Object Storage API service. Unless you have a
 # custom Keystone service catalog implementation, you probably want to leave