Print _log clusters_ periodically or on a signal or key combination

[bric3]

Currently in drain mode, the discovered log clusters are only dumped (printed) when the log file has been entirely read.

This is not suitable when it is needed to watch a log file, there should be some mechanism to print the clusters

• Periodically, with a flag on the command line to tweak the interval
• Allows to handle a signal (maybe allowing to pick a signal from the os supported signal kill -l, without overriding the standard ones that are handled by the JVM already)
• In the running tty, send a key combination, like ctrl+d