ksqlDB should indicate if no connector tasks are running

[rmoff]

ksql> show connectors;

 Connector Name | Type | Class                                       | Status
---------------------------------------------------------------------------------------------------
 SINK_INFLUX_03 | SINK | io.confluent.influxdb.InfluxDBSinkConnector | RUNNING (1/1 tasks RUNNING)
 SINK_INFLUX_04 | SINK | io.confluent.influxdb.InfluxDBSinkConnector | RUNNING (0/1 tasks RUNNING)

IMO the SINK_INFLUX_04 connector should show something to indicate that there might be a problem, e.g.

ksql> show connectors;

 Connector Name | Type | Class                                       | Status
---------------------------------------------------------------------------------------------------
 SINK_INFLUX_03 | SINK | io.confluent.influxdb.InfluxDBSinkConnector | RUNNING (1/1 tasks RUNNING)
 SINK_INFLUX_04 | SINK | io.confluent.influxdb.InfluxDBSinkConnector | WARNING (0/1 tasks RUNNING)

WDYT @agavra ?

[ybyzek]

Just to differentiate related issues:

1. It should highlight there is a problem with the connector/task
2. It should surface the exact error or reason why the connect worker failed --> Surface errors from Connect workers #3775
3. It should surface the exact error or reason why the connector/task failed --> should this be separate from Surface errors from Connect workers #3775 ?