Same peer explanation appears more than once

[kitsook]

When the "Answers Students See - Number Selected" options is set to be bigger than number of answers, same peer explanation may appear more than once in Step 2.

Need to check the answer pool logic.

Edit: it happens when the selection logic is Simple

ubcpi/ubcpi/answer_pool.py

Lines 252 to 260 in ff69bbb

	i = 0
	while (student == student_id or i > 100) and (str(option) + student) not in selected:
	# retry until we got a different one or after 100 retries
	# we are suppose to get a different student answer or a seeded one in a few tries
	# as we have at least one seeded answer for each option in the algo. And it is not
	# suppose to overflow i order to break the loop
	student = random.choice(students.keys())
	i += 1
	selected.append(str(option)+student)