To most of us, a cold bubble bath outside at 8 a.m. doesn’t exactly sound appealing. But add some yummy raw chicken treats and an encouraging caregiver, and Rainier the wolverine was ready and willing. But this wasn’t just a fun spa day. The bath was part of a months-long training to let the furry wolverine help his human team at Northwest Trek Wildlife Park care for his itchy skin. “Hi, boy!” called keeper Wendi Mello, as she walked up to the undercover “bedrooms” where the wolverines spent each night. Rainer instantly ran up to the mesh, face curious and …