Lansdale officials hope to reopen White's Road Pool this weekend after it was unexpectedly shutdown last Sunday because of plaster dust suspended in the water.   The residue was leftover from maintenance work at the facility.   Borough officials say even though the situation was unavoidable pool members will still get their money's worth.   They have decided to open both the White's Road Pool and the Fourth Street Pool an hour early every Sunday in July.   The White's Road Pool will also be open an extra weekend after the season would normally end on Labor Day.