Node.js agent v2.5.0

Added hapi v17 instrumentation
Hapi v17 added support for promise-based middleware which broke transaction tracking in the agent. This caused issues in naming, as the agent will name the transaction after the path to the middleware that responded to a request.
Added instrumentation for vision@5
Due to the way vision is mounted to the hapi server when using hapi v17.x, the agent's instrumentation would not pick up on the middleware being mounted. This new instrumentation now correctly times rendering done in the vision middleware.
Added unwrapOnce method to shim object
This new method can be used to unwrap a single layer of instrumentation. unwrapOnce is useful in cases where multiple instrumentations wrap the same method and unwrapping of the top level is required.
Added isErrorWare checks around nameState.appendPath/nameState.popPath calls to avoid doubling up paths in transaction names
Previously, the agent would append its transaction name with the path fragment where an error handler middleware was mounted. The extraneous path fragment will now be omitted, and the transaction will be named properly after the middleware that threw the error.
Added support for pg 6 on Node 5 or higher

Added parent property to webframework-shim segment description
Refactored existing hapi instrumentation for different server.ext() invocations
Refactored webframework-shim _recordMiddleware to construct different segment descriptions for callback- or promise-based middleware
Updated node-postgres@^6 versioned tests to avoid deprecation warning on direct module connect and end calls
Fixed running domain tests on Node 9.3.0.
Improved logging for CAT headers and transaction name-state management.
All json-safe-stringify calls now wrapped in try/catch
Removed lib/util/safe-json

Fixed creating supportability metric when mysql2 goes uninstrumented.
Added a segmentStack.popto the middleware after in cases when an error is caught and there is no next handler
Fixed determining parents for middleware segments when transaction state is lost and reinstated
Added check to _recordMiddleware to avoid prepending a slash if original route is an array
Changed logic in http instrumentation to attach response.status to the transaction as a string
Updated startWebTransaction and startBackgroundTransaction to add nested transactions as segments to parent transactions