generic/478: fix potential test blocking

Reduce semtimedop timeout to 5s, 15s is too long if something get
tangled up. Add retry counting to getlk routine, infinite loop is
dangerous. If something goes wrong unexpextedly, test is blocked and
wasting time.

Signed-off-by: Xiong Zhou <xzhou@redhat.com>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>