Fix: tools, libcrmcommon: Reopen the output dest on reset.

This is needed when running crm_mon as a daemon. When we do a reset,
we need to clear out any existing output destination and start writing
again from the beginning. This really only matters when the destination
is a file.

The extra freopen at the end of crm_mon is to handle when crm_mon is
killed. We need to reset the output file to its beginning before
calling finish.