<!--- Verify first that your feature was not already discussed on GitHub -->
<!--- Complete *all* sections as described, this form is processed automatically -->

##### SUMMARY
<!--- Describe the new feature/improvement briefly below -->
This feature would implement a ClearSessions command for the Sessions category of redfish_command, to clear all active sessions.

##### ISSUE TYPE
- Feature Idea

##### COMPONENT NAME
<!--- Write the short name of the module, plugin, task or feature below, use your best guess if unsure -->
redfish_command.py
redfish_utils.py

##### ADDITIONAL INFORMATION
<!--- Describe how the feature would be used, why it is needed and what it would solve -->
This command would help user to clear all active sessions.

<!--- Paste example playbooks or commands between quotes below -->
```yaml

```

<!--- HINT: You can also paste gist.github.com links for larger files -->

response = self.get_request(self.root_uri + self.service_root)
        if response['ret'] is False:
            return response
        data = response['data']
        if 'SessionService' not in data:
            return {'ret': False, 'msg': "SessionService resource not found"}
        else:
            session_service = data["SessionService"]["@odata.id"]
            response = self.get_request(self.root_uri + session_service)
            if response['ret'] is False:
                return response
            data = response['data']
            sessions = data['Sessions']['@odata.id']
            if sessions[-1:] == '/':
                sessions = sessions[:-1]
            self.sessions_uri = sessions
        return {'ret': True}
    def _get_resource_uri_by_id(self, uris, id_prop):
        for uri in uris:
            response = self.get_request(self.root_uri + uri)
            if response['ret'] is False:
                continue
            data = response['data']
            if id_prop == data.get('Id'):
                return uri
        return None
    def _find_systems_resource(self):