stall-analyser: add direction option
stall-analyser: add direction option

By default, print the graph top-down, i.e. callers first.
Alternatively --direction bottom-up will print the graph
in "stack" order, callees first.

Signed-off-by: Benny Halevy <23c997c90eb8537635e9392d48e7af1bf1b2ca22@scylladb.com>

scylladb/seastar,avikivity/seastar,cloudius-systems/seastar,syuu1228/seastar,cloudius-systems/seastar,avikivity/seastar,syuu1228/seastar,scylladb/seastar,syuu1228/seastar,cloudius-systems/seastar,scylladb/seastar,avikivity/seastar