loader.py: Make 'osv trace duration' not sorted by default

This patch adds sorting as an option (-s). Examples:

 Not sorted:

   gdb$ osv trace duration

 Sorted, narrowed down to one function:

   gdb$ osv trace duration -s vfs_pwritev

Not sorting allows us to start printing traces right away. There's
also no need to keep them in memory, which makes the command a bit
faster.

Signed-off-by: Tomasz Grabiec <tgrabiec@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>