Fixes #8519 - Bonus subs not being reindexed

Bonus subscriptions aren't being reindexed since the handler was only
watching for entitlements that got created/deleted. Handler should be
watching pool create/delete.
@thomasmckay sometimes I get the message before the pool is available in candlepin...so when I query the pool in cp, it would throw a ResourceNotFound error...it was causing end-to-end testing to be inconsistent.