selftest: Make setexpiry test much more reliable

selftest: Make setexpiry test much more reliable

Rather than setting all the expiries and expecting that they will be done within 5 seconds,
measure and check the time individually for each record.

This should make this test much less prone to flapping.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=13867

Signed-off-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Gary Lockyer <gary@catalyst.net.nz>
Autobuild-User(master): Andrew Bartlett <abartlet@samba.org>
Autobuild-Date(master): Tue May 15 23:58:17 CEST 2018 on sn-devel-144

(cherry picked from commit 5ebe3183fded1ab060ed60baeedeac859d0c137e)

Autobuild-User(v4-8-test): Karolin Seeger <kseeger@samba.org>
Autobuild-Date(v4-8-test): Tue Apr  2 15:16:10 UTC 2019 on sn-devel-144