FO: Use SRV TTL in fail over code
Resolves:
https://fedorahosted.org/sssd/ticket/1884
Removes the hardcoded SRV TTL timeout and uses TTL from the DNS instead.
Reviewed-by: Pavel Březina <pbrezina@redhat.com>
(cherry picked from commit 8df69bbc58c2f4d3f0b34be9756d9ddf24b1db6d)