InfluxDB Publisher can hang forever if InfluxDB unavailable

[BrianJKoopman]

At least one (perhaps several) situations can arise in the InfluxDB Publisher where the Agent will not stop properly if the InfluxDB itself isn't available. For example, if the database isn't available on startup the Agent waits for it to become available before moving on, preventing proper shutdown of the Agent. This situations should be eliminated, perhaps trying a number of times before giving up and exiting the Agent, depending on the situation.