Fix doc issue of lock test accounts

When using the lock testing accounts, allow_tenant_isolation
should be set as False. Now it's missing in the document.
This patch will add it.

Closes-Bug: #1454001

Change-Id: I3e1e7a31ea4c1c8b25e821df545c8674a8de38da
diff --git a/doc/source/configuration.rst b/doc/source/configuration.rst
index b6e00ce..b434fdc 100644
--- a/doc/source/configuration.rst
+++ b/doc/source/configuration.rst
@@ -115,6 +115,8 @@
  #. Provide tempest with the location of you accounts.yaml file with the
     test_accounts_file option in the auth section
 
+ #. Set allow_tenant_isolation = False in the auth group
+
 It is worth pointing out that each set of credentials in the accounts.yaml
 should have a unique tenant. This is required to provide proper isolation
 to the tests using the credentials, and failure to do this will likely cause
@@ -140,6 +142,11 @@
  #. alt_password
  #. alt_tenant_name
 
+And in the auth secion:
+
+ #. allow_tenant_isolation = False
+ #. comment out 'test_accounts_file' or keep it as empty
+
 It only makes sense to use it if parallel execution isn't needed, since tempest
 won't be able to properly isolate tests using this. Additionally, using the
 traditional config options for credentials is not able to provide credentials to