tests/tls_test: Ensure resources are closed and futures are waited for
tests/tls_test: Ensure resources are closed and futures are waited for

This patch contains several fixes to tls_test, to ensure that streams
are always closed and futures are waited for.

Signed-off-by: Duarte Nunes <a60e8b7496f7715d71354fe4c06dd24017025bf1@scylladb.com>

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