trace: show thread name in 'trace.py prof'

Applies when grouping by thread.

Before:

  === Thread 0xffff8001170c3050 ===

After:

  === Thread >>>>>>>java.so (0xffff8001170c3050) ===

Signed-off-by: Tomasz Grabiec <tgrabiec@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
zfs: add missing ZFS_EXIT()

Not that it fixes something since ZFS_EXIT is currently no-op on OSv
but if one day we would like to bring it back this would matter.

Signed-off-by: Tomasz Grabiec <tgrabiec@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
trace: show thread's name in list-timed output

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