Introduce reset handler

This change introduces a reset handler which encapsulates the
setting and handling of resetting signals, and the actual counter resetting.
This cleans up the do_md loop, exchanging several lines of code by
a single command. It also makes a step towards a task-based design by
only calling the internal functions when necessary (if counter resetting
was requested, signal setting only on master).

Refs #1793

Change-Id: I5dec051cd3a0c0b3b52dfe69a72dac7f7e9f65ed