Fixes on editing cluster configuration

[adri9valle]

Hi team,

Testing this issue #551, if set in the ossec.conf:

<cluster>
...
<disabled>yes</disabled>
...
</cluster>

On the master node when the cluster status is running yet, if the configuration is saved and click on the restart button from the confirm dialog, is launched an error because the APP tries to check the node configuration with this API call: /cluster/{node_master_name}/configuration/validation this are incorrect because in the ossec.conf the cluster is disabled, then the API won't answer to this call launching an error. This was fixed checking if the cluster is disabled the check is launched against the manager.

Also, have been removed the abstract state of management fixing that sometimes the Edit configuration button disappear.

Regards,