log:tail threads keep running after ssh exits

When executing `log:tail` via Karaf's ssh connection, the created thread is not killed when the ssh connection is killed or timeouts. Steps to reproduce: * Open a ssh connection with Karaf * Run `log:tail` * Either close the session without exiting `log:tail` or wait until it timeouts in a few minutes * Run shell:threads | grep log:tail on the console or another ssh connection * A log tail thread is still running. * Every time this process is repeated, a new `log:tail` thread will appear and stay alive.