(Adds media codes, fixes spelling in paragraph 4) JERUSALEM (Reuters) -At the end of a kilometer-long, booby-trapped tunnel in the Gaza Strip, Israeli soldiers discovered cramped cells where the military said Hamas kept about 20 hostages. They found a holding area, five narrow rooms behind metal bars, toilets, mattresses, and even drawings by a child hostage who was freed during a November truce, military spokesman Rear Admiral Daniel Hagari said. No hostages were there when it was discovered. The military released photos from the underground labyrinth and said it brought in journalists to doc…