Quiz report should use user's preference of CSV

[Gao-Jun]

While generating quiz report, the generated CSV file doesn't use the user's preference of CSV. This patch fix this issue.

Test plan

• Update user preference of CSV, use semicolon(;) as separator.
• Create a new quiz, and have a submission. (quiz with no submission can not be exported)
• Export 'Student Analysis' or 'Item Analysis' of this quiz.

Expected The exported CSV file should use semicolon(;) as separator

Actual result The exported CSV file still use comma(,) as separator