100MB files would take less than a second to sync, which makes no difference
in 'last_synced_end' and the test fails intermittently. We need to increase the
size of the files, as the time/duration is determined only in seconds.
Because of this, it also needs more sleep time before checking the status.
Fixes: https://tracker.ceph.com/issues/69232 Signed-off-by: Jos Collin <jcollin@redhat.com>