Back from a summer of fun and the life-changing “Frozen” documentary, the Wildcats are intent to settle back into a drama-free school year and put on a stage production of  “High School Musical 3: Senior Year.” But when Disney announces that “High School Musical 4: High School Reunion” will be shooting at East High with hotshot new teen stars and the O.G. Wildcat gang bringing Hollywood drama, the status quo is upended forever.