MRP-1741 tests: fix test numeration

Rename test_160 and test_16oc to test_160a and test_160c according to
test numeration policy.

Change-Id: If53ac1c3a6e67aa429e04b20d827ee94dc1d9e3d
Signed-off-by: Vladimir Saveliev <vladimir_saveliev@xyratex.com>
Reviewed-on: http://es-gerrit.xyus.xyratex.com:8080/1659
Tested-by: Jenkins
Reviewed-by: Denis Kondratenko <denis_kondratenko@xyratex.com>
Reviewed-by: Elena Gryaznova <elena_gryaznova@xyratex.com>
Tested-by: Elena Gryaznova <elena_gryaznova@xyratex.com>
Reviewed-by: Vitaly Fertman <vitaly_fertman@xyratex.com>