HPCC-12226 Push kernel message info new section of workunit

Add a virtual to IPerfMonHook to allow kernel logs captured by
the monitor to be redirected.
Implement a hook method that fires the kernel messages to a
'Alert' section in the workunit.
Default to capturing kernel message of level <=3, which means
KERN_EMERG, KERN_ALERT, KERN_CRIT, KERN_ERR.

Also slightly reorganize the job start/end to common up the
monitoring between slave and master.
Also add a Origin for Thor exceptions, so can more easily see
which slave or master they came from.

Signed-off-by: Jake Smith <jake.smith@lexisnexis.com>
(it's an odd convention though - not entirely sure why it was adopted)