* remove dead code (from .yy)
* remove redundant commands from the test
* extract common code into a reusable function
  (get_auth_plugin, push_new_user)
* rename update_user_table->update_user_table_password
* simplify acl_update_user
* don't strdup a string that's already in a memroot
  (in ACL_ROLE::ACL_ROLE(ACL_USER*))
* create parent_grantee and role_grants dynamic arrays with size 0.
  to avoid any memory allocations when roles aren't used.