dtrace: improve probe execution debugging

dtrace: improve probe execution debugging

The debugging code for probe execution had a few cases were the start
of execution was logged in debugging output but the completion was not
because of early termination conditions.  Now all forms of completion
should be covered in debugging output.

Signed-off-by: Kris Van Hees <kris.van.hees@oracle.com>
Reviewed-by: Tomas Jedlicka <tomas.jedlicka@oracle.com>
Reviewed-by: Nick Alcock <nick.alcock@oracle.com>