Remove references to locking test accounts config doc

The name locking test accounts was an early name in the development of
the pre-provisioned credentials development. It described what it did
used tests accounts and lock files to ensure one test class only was
using an account at a time. However, that name hasn't been really used
in a long time and we've called the feature pre-provisioned credentials.
The configuration guide section for pre-provisioned credentials still
had some out dated references to locking test accounts which were never
updated when the feature was renamed. This commit corrects the oversight
and consistently names the feature in that section of the documentation.

Change-Id: I0f3a7b373c5ca2d84a8e82c1e2c3bcd6a2d833f9

doc/source/configuration.rst

@@ -108,12 +108,12 @@ wanted to enable parallel execution of Tempest tests. However, this was
 insufficient for certain use cases because of the admin credentials requirement
 to create the credential sets on demand. To get around that the accounts.yaml
 file was introduced and with that a new internal credential provider to enable
-using the list of credentials instead of creating them on demand. With locking
-test accounts each test class will reserve a set of credentials from the
-accounts.yaml before executing any of its tests so that each class is isolated
-like with dynamic credentials.
+using the list of credentials instead of creating them on demand. With
+pre-provisioned credentials (also known as locking test accounts) each test
+class will reserve a set of credentials from the accounts.yaml before executing
+any of its tests so that each class is isolated like with dynamic credentials.
 
-To enable and use locking test accounts you need do a few things:
+To enable and use pre-provisioned credentials you need do a few things:
 
 #. Create an accounts.yaml file which contains the set of pre-existing
    credentials to use for testing. To make sure you don't have a credentials