directories: Do touch_and_lock and verify sequentially
directories: Do touch_and_lock and verify sequentially

The goal is to drop the seastar::async() usage.

Currently we have two places that return futures -- calls to
parallel_for_each-s.  We can either chain them together or,
since both are working on the same set of directories, chain
actions inside them.

For code simplicity I propose to chain actions.

Signed-off-by: Pavel Emelyanov <c9a32589e048e044184536f7ac71ef92fe82df3e@scylladb.com>

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