Tomas Hertl and Logan Couture both scored third-period goals and goalie Kaapo Kahkonen led a brilliant penalty kill as the San Jose Sharks opened a four-game road trip Tuesday with a 4-0 win over the Montreal Canadiens at the Bell Centre. The Sharks, with the NHL’s best penalty kill, erased all six Canadiens’ power plays, including a two-man advantage that expired early in the third period. Kahkonen finished with 28 saves, including four while the Sharks were shorthanded, as he earned the third shutout of his career and his first in San Jose. “That’s great, but it also tells tell a lot about t…