Fix role readme

Lately we added a flavor autodiscover feature and due to that
we edited generate-tempestconf-file role.
The patch removes unused registered variable and edits readme.

Change-Id: Ibf55d35ab00aafd0b7efe83805f1a96f11fe2f0a

roles/generate-tempestconf-file/README.rst

@@ -67,10 +67,8 @@ is then copied to tempest directory.
 
    If checking of demo user abilities is desired to be enabled, set this
    variable to True.
-   When True, a set of tasks, where generation of tempest configuration is
-   intended to fail, is included. The set includes also tasks, which create
-   tempest resources. After that, the generation of the tempest configuration is
-   suppossed to pass.
+   When True, a set of tasks for testing demo user is included. The set
+   includes tasks, which create necessary tempest resources.
    NOTE: If the variable is set to True, it's needed to set cloud_admin variable
    as well, see info below.
 

roles/generate-tempestconf-file/tasks/test-demo-user.yaml

@@ -4,7 +4,6 @@
     args:
       chdir: "{{ tempestconf_src_relative_path }}"
       executable: /bin/bash
-    register: result
 
   - name: Create m1.nano and m1.micro flavors for demo user
     shell: |