As part of upgrading boost in SERVER-70000, the behavior of boost's hashing functionality is changing. boost notably does not guarantee the stability of hash values across versions. As a result, tests that require PlanCacheKey and QuerySettingsHash to be stable will have to be adjusted every time the hashing behavior changes because they use boost to calculate hashes. We should consider arriving at a stable hash implementation (perhaps by implementing it ourselves or vendoring it from elsewhere) and porting PlanCacheKey and QuerySettingsHash (and any other hashes that need to be stable) to use that stable hash implementation. We appear to already have an implementation of murmur hash; it might be sufficient to just use that.