Merge pull request #2106 from raydavis/qawip

CLC-2896 Use student-specific view for get_enrolled_students query
CLC-3274 Feature flag for delayed cache cleaner, defaulting to enabled
Merge pull request #2118 from ctweney/clc-3274-qa

CLC-3274 Feature flag for delayed cache cleaner, defaulting to enabled
CLC-3273 Do not treat Canvas existence checks as unexpected errors