scylla_io_setup: assume default directories under /var/lib/scylla
scylla_io_setup: assume default directories under /var/lib/scylla

If a specific directory is not configure in scylla.yaml, scylla assumes
a default location under /var/lib/scylla.

Hard code these locations in scylla_io_setup until we have a better way
to probe scylla about it.

Be permissive and ignore the default directories if they don't not exist
on disk and silently ignore them.

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

scylladb/scylla,avikivity/scylla,scylladb/scylla,avikivity/scylla,avikivity/scylla,scylladb/scylla,scylladb/scylla