tests/unit/exception_loggin_test.cc: add a nested std::system_error use case
tests/unit/exception_loggin_test.cc: add a nested std::system_error use case

Test that a nested exception chain is properly unrolled
in the case when std::system_error is in the middle of it.

Signed-off-by: Vlad Zolotarov <976c0f8d0852ed6439ad273880b400a75a7c41d0@scylladb.com>

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