[tests] allow extra chars in prefix list 'wpanctl' output (#6240)
[tests] allow extra chars in prefix list 'wpanctl' output (#6240)

This commit relaxes the parsing of on-mesh prefix list `wpanctl`
output in `wpan.py` allowing extra chars to be present between
"pref:" and "prio:".
srickardti/openthread,openthread/openthread,openthread/openthread,abtink/openthread,jwhui/openthread,jwhui/openthread,jwhui/openthread,abtink/openthread,abtink/openthread,openthread/openthread,srickardti/openthread,srickardti/openthread,jwhui/openthread,srickardti/openthread,abtink/openthread,openthread/openthread