What is the percentage of complaints about the late fee issue whose priority is 2 in 2017?
percentage = divide(count(Complaint ID where priority = 2) , count(Complaint ID)) * 100%; in 2017 refers to year(Date received) = 2017
SELECT CAST(SUM(CASE WHEN T1.priority = 2 THEN 1 ELSE 0 END) AS REAL) * 100 / COUNT(T1.`Complaint ID`) FROM callcenterlogs AS T1 INNER JOIN events AS T2 ON T1.`Complaint ID` = T2.`Complaint ID` WHERE strftime('%Y', T1.`Date received`) = '2017'