The server should not be polled when an error or timeout is detected

The ``retrieve_cached_meeting_info method``` of the meeting instance caches the current data for a meeting.
This is prevents Moodle from querying the Bigbluebutton server every time a student want to know the meeting's status.
However, if we disconnect the Bigbluebutton server AND the cache expires, then each student query will also try to retrieve the information on the BigblueButton server.
If the BBB server is slow to answer this might lead to a lot of queries being left pending on the Moodle side, which means that it will load the Moodle server unnecessarily.

The aim of this ticket is:

• To make sure that when we fetch info from the BBB server and either there is an error (we detect the server is down) or the query times
  out, the we prevent other queries from being sent, at least for some time.
• We display an error status on each BBB meeting so the user is aware that there is an issue on the server.