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>