Add regression tests for bugs 220459 and 220398

Bug 220398 - lio_listio(2) never sends asynchronous notification if nent==0
Bug 220459 - lio_listio(2) doesn't support SIGEV_THREAD

PR: 220459
PR: 220398
Reviewed by: cem, jhb
MFC after: 3 weeks
Sponsored by: Spectra Logic Corp
Differential Revision: https://reviews.freebsd.org/D11470