Better error handling if InfluxDB-database is not accessible

[dmuravov]

A. Setup:

1. JMeter-testplan checks a REST-API of a server-side software
2. HTTP-Request blocks are used to send REST-calls
3. Every ThreadGroup has a BackendListener to write into a time-series database.
4. Such a BackendListener uses a JMeter plugin "JMeter-InfluxDB-Writer 1.2".

B. Test execution:

1. JMeter is started with Maven (meter-maven-plugin:2.8.1).
2. If the InfluxDB is not reachable for JMeter then an IllegalStateException is thrown
3. After that a row of Timeout-errors come (which is understandable).
4. JMeter hangs and never stops (as experiment I have waited for 2 hours).

C. My proposal:

1. If something wrong happens in the startup phase with the Sampler-block then break the test with an error message.
2. If something wrong happens with a supporting "secondary" element like a Backend-Listener then catch the exception, stop the execution and show a warning with a hint for the user to deactivate Backend-Listener with a passed property say "backend.listener.disabled=true" or fix the connection issue.

Reason for (2) is that developers use sometimes JMeter on their local machines without having set up (or having access to) all "add-ons" like a time-series database etc. They just want to verify quickly their changes in code and get simple feedback from JMeter in form of response times without any further statistic collection.

Example of the unhandled error is in the log-file.
jmeter_error.log