Generate random keystone users

Depends-On: https://gerrit.mcp.mirantis.com/#/c/44319/
Depends-On: https://gerrit.mcp.mirantis.com/#/c/45118/
Depends-On: https://gerrit.mcp.mirantis.com/#/c/45119/

Related-Prod: PROD-29868
Related-Prod: PROD-31315
(cherry picked from commit f5956c2f6151cc5d99659103f90641ea66eac44a)
(cherry picked from commit 70dd0f0587eb297fbefdea43837839c4983b8378)

Change-Id: I402be73437d5397224184a4fd71e2f6abae24db2
diff --git a/keystone/server/single.yml b/keystone/server/single.yml
index 014a6dc..8c5e594 100644
--- a/keystone/server/single.yml
+++ b/keystone/server/single.yml
@@ -43,7 +43,7 @@
         host: ${_param:single_address}
         name: keystone
         password: ${_param:mysql_keystone_password}
-        user: keystone
+        user: ${_param:mysql_keystone_username}
         x509:
           enabled: ${_param:openstack_mysql_x509_enabled}
           ca_file: ${_param:mysql_keystone_ssl_ca_file}