build.mk: move modules/tests/usr.manifest to build/

Move modules/tests/usr.manifest into build/$(mode)/
The modules/tests/usr.manifest file is generated during 'make image=tests' and appears
as untracked in 'git status'. Moving it inside build/ gets rid of the message.

Signed-off-by: Jaspal Singh Dhillon <jaspal.iiith@gmail.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
top.py: add tie-breaker sort criterion

Usually we have just a few threads with non-zero CPU usage, and the rest
are tied at 0%. Add a secondary sorting criterion, which is the total
CPU time. So now after all the threads using CPU now, we see the threads
that have been using a lot of CPU time in the past, instead of just a bunch
of random threads.

Reviewed-by: Tomasz Grabiec <tgrabiec@gmail.com>
Signed-off-by: Nadav Har'El <nyh@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>