sd: use the correct default for LEASE_TIME_SEC

Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1011505
Change-Id: I7d0e3939241120656513d47d1bbb1cacaef0ae83
Signed-off-by: Federico Simoncelli <fsimonce@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/19567
Tested-by: Ohad Basan <obasan@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>