Point operators to logs when instance is not clustered

Never report "None" as the cluster status. Rather, acknowledge the instance is not clustered and point the operator to the logs for further investigation.

There are a number of circumstances that can lead to an instance not successfully being joined to the cluster.

Example [0]

mysql-innodb-cluster/1 active executing 2 172.17.110.3 Unit is ready: Mode: R/W
mysql-innodb-cluster/2* active executing 3 172.17.110.33 Unit is ready: Mode: R/O
mysql-innodb-cluster/4 blocked idle 6 172.17.110.30 MySQL InnoDB Cluster not healthy: None

Example [1]

Unit Workload Agent Machine Public address Ports Message
mysql-innodb-cluster/0* blocked idle 0 10.5.0.7 MySQL InnoDB Cluster not healthy: Cluster has no quorum as visible from '10.5.0.7:3306' and cannot process write transactions. 2 members are not active
mysql-innodb-cluster/1 blocked idle 1 10.5.0.18 MySQL InnoDB Cluster not healthy: None
mysql-innodb-cluster/2 blocked idle 2 10.5.0.9 MySQL InnoDB Cluster not healthy: None

Currently, the workload status shows "MySQL InnoDB Cluster not healthy: None" which is not helpful. This also leads to bugs being filed on the work load status rather than the root cause of the failure to cluster.

The work load status of an unclustered instance should point the operator to investigate the logs or report the root cause error.

Note: The change will need to avoid false positives as much as possible for expected circumstances as in during deploy time or scale in scale out testing.

[0] https://bugs.launchpad.net/charm-mysql-innodb-cluster/+bug/1889792
[1] https://bugs.launchpad.net/charm-mysql-innodb-cluster/+bug/1917332