Swap use -> require in resolve-symbol helper

[DaoWen]

Changes proposed in this PR

Use require rather than symbol for our our dynamic "class-loading" logic in the resolve-symbol helper (the function that we use for loading :factory-fns for Waiter components.)

Why are we making these changes?

Since use imports all members into the current namespace, that was causing errors when we use the waiter.auth.kerberos namespace twice: once for Authentication, and once for Authorization. The conflicts were causing fatal errors on Waiter startup.