Use smaller writes for fstrim test
Use smaller writes for fstrim test

Should speed things up, and reduce the chance we'll hit timeouts.

Signed-off-by: Maya Rashish <309f5d63d2311d00fe13deb09dd851fb2714413c@redhat.com>

kubevirt/kubevirt,kubevirt/kubevirt,kubevirt/kubevirt,kubevirt/kubevirt