Use augments to enable HA instead of modifying policy

We instruct people to use the preffered way of defining custom
classes on hosts even when enabling HA.

(cherry picked from commit 3ec7939)

enterprise-cfengine-guide/high-availability/installation-guide.markdown

@@ -513,18 +513,15 @@ HA fencing guide](https://access.redhat.com/documentation/en-us/red_hat_enterpri
 
    **IMPORTANT:** Copy over only the hashes, without the `SHA=` prefix.
 
-6. **On both nodes,** modify the */var/cfengine/masterfiles/controls/def.cf* and
-   */var/cfengine/masterfiles/controls/update_def.cf* files to enable HA by uncommenting the
-   following line:
+6. **On both nodes,** add the following class definition to the */var/cfengine/masterfiles/def.json*
+   file to enable HA:
 
    ```
-   "enable_cfengine_enterprise_hub_ha" expression => "enterprise_edition";
-   ```
-
-   and commenting or removing the line
-
-   ```
-   "enable_cfengine_enterprise_hub_ha" expression => "!any";`
+   {
+     "classes": {
+       "enable_cfengine_enterprise_hub_ha": [ "any::" ]
+     }
+   }
    ```
 
 7. **On both nodes,** run `cf-agent -Kf update.cf` to make sure that the new policy is copied from