[tests] attempt to fix intermittent failures of MATN-12 (#6858)
[tests] attempt to fix intermittent failures of MATN-12 (#6858)

The test failed because the script failed to read the output of ipaddr
rloc. This can be fixed by adding some wait time at the end of the
test.
abtink/openthread,jwhui/openthread,jwhui/openthread,openthread/openthread,openthread/openthread,srickardti/openthread,abtink/openthread,openthread/openthread,openthread/openthread,abtink/openthread,srickardti/openthread,jwhui/openthread,jwhui/openthread,abtink/openthread,srickardti/openthread,srickardti/openthread