User Guide examples can have long runtimes

[trevorhardy]

I'd like to investigate the cause of the long run times in some/many/all of the HELICS examples and see if there's something simple we can do to reduce the runtimes.

[trevorhardy]

I've done some initial testing showing that changing the logging level to "INFO" cuts the runtime in half and dramatically reduces the size of the log files. I would be in favor of making this change across the board with a few caveats:

1. We will need to be consistent across the examples about which messages get logged at which levels so that user's have a consistent experience.
2. It would be good to be able to change the logging level on the command line.
3. Right now, when I change the log level, the examples don't always run to completions (see this Github issue).